* Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux [not found] <18980.48553.328662.80987@notabene.brown> @ 2009-06-02 20:11 ` Jeff Garzik 2009-06-02 22:58 ` Dan Williams 2009-06-03 3:56 ` Neil Brown 0 siblings, 2 replies; 10+ messages in thread From: Jeff Garzik @ 2009-06-02 20:11 UTC (permalink / raw) To: Neil Brown; +Cc: linux-raid, LKML, linux-fsdevel, Arjan van de Ven, Alan Cox Neil Brown wrote: > > I am pleased to (finally) announce the availability of > mdadm version 3.0 > > It is available at the usual places: > countrycode=xx. > http://www.${countrycode}kernel.org/pub/linux/utils/raid/mdadm/ > and via git at > git://neil.brown.name/mdadm > http://neil.brown.name/git?p=mdadm > > > This is a major new version and as such should be treated with some > caution. However it has seen substantial testing and is considerred > to be ready for wide use. > > > The significant change which justifies the new major version number is > that mdadm can now handle metadata updates entirely in userspace. > This allows mdadm to support metadata formats that the kernel knows > nothing about. > > Currently two such metadata formats are supported: > - DDF - The SNIA standard format > - Intel Matrix - The metadata used by recent Intel ICH controlers. This seems pretty awful from a support standpoint: dmraid has been the sole provider of support for vendor-proprietary up until this point. Now Linux users -- and distro installers -- must choose between software RAID stack "MD" and software RAID stack "DM". That choice is made _not_ based on features, but on knowing the underlying RAID metadata format that is required, and what features you need out of it. dmraid already supports - Intel RAID format, touched by Intel as recently as 2007 - DDF, the SNIA standard format This obviously generates some relevant questions... 1) Why? This obviously duplicates existing effort and code. The only compelling reason I see is RAID5 support, which DM lacks IIRC -- but the huge issue of user support and duplicated code remains. 2) Adding container-like handling obviously moves MD in the direction of DM. Does that imply someone will be looking at integrating the two codebases, or will this begin to implement features also found in DM's codebase? 3) What is the status of distro integration efforts? I wager the distro installer guys will grumble at having to choose among duplicated RAID code and formats. 4) What is the plan for handling existing Intel RAID users (e.g. dmraid + Intel RAID)? Has Intel been contacted about dmraid issues? What does Intel think about this lovely user confusion shoved into their laps? 5) Have the dmraid maintainer and DM folks been queried, given that you are duplicating their functionality via Intel and DDF RAID formats? What was their response, what issues were raised and resolved? Jeff ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-02 20:11 ` ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux Jeff Garzik @ 2009-06-02 22:58 ` Dan Williams 2009-06-03 3:56 ` Neil Brown 1 sibling, 0 replies; 10+ messages in thread From: Dan Williams @ 2009-06-02 22:58 UTC (permalink / raw) To: Jeff Garzik Cc: Neil Brown, linux-raid, LKML, linux-fsdevel, Arjan van de Ven, Alan Cox, Ed Ciechanowski, Jacek Danecki On Tue, Jun 2, 2009 at 1:11 PM, Jeff Garzik <jeff@garzik.org> wrote: > Neil Brown wrote: >> >> I am pleased to (finally) announce the availability of >> mdadm version 3.0 >> >> It is available at the usual places: >> countrycode=xx. >> http://www.${countrycode}kernel.org/pub/linux/utils/raid/mdadm/ >> and via git at >> git://neil.brown.name/mdadm >> http://neil.brown.name/git?p=mdadm >> >> >> This is a major new version and as such should be treated with some >> caution. However it has seen substantial testing and is considerred >> to be ready for wide use. >> >> >> The significant change which justifies the new major version number is >> that mdadm can now handle metadata updates entirely in userspace. >> This allows mdadm to support metadata formats that the kernel knows >> nothing about. >> >> Currently two such metadata formats are supported: >> - DDF - The SNIA standard format >> - Intel Matrix - The metadata used by recent Intel ICH controlers. > > This seems pretty awful from a support standpoint: dmraid has been the sole > provider of support for vendor-proprietary up until this point. This bares similarities with the early difficulties of selecting between ide and libata. > Now Linux users -- and distro installers -- must choose between software > RAID stack "MD" and software RAID stack "DM". That choice is made _not_ > based on features, but on knowing the underlying RAID metadata format that > is required, and what features you need out of it. > > dmraid already supports > - Intel RAID format, touched by Intel as recently as 2007 > - DDF, the SNIA standard format > > This obviously generates some relevant questions... > > 1) Why? This obviously duplicates existing effort and code. The only > compelling reason I see is RAID5 support, which DM lacks IIRC -- but the > huge issue of user support and duplicated code remains. The MD raid5 code has been upstream since forever and already has features like online capacity expansion. There is also infrastructure, upstream, for online raid level migration. > 2) Adding container-like handling obviously moves MD in the direction of DM. > Does that imply someone will be looking at integrating the two codebases, > or will this begin to implement features also found in DM's codebase? I made a proof-of-concept investigation of what it would take to activate all dmraid arrays (any metadata format, any raid level) with MD. The result, dm2md [1], did not stimulate much in the way of conversation. A pluggable architecture for a write-intent log seems to be the only piece that does not have a current equivalent in MD. However, the 'bitmap' infrastructure covers most needs. I think unifying on a write-intent logging infrastructure is a good place to start working together. > 3) What is the status of distro integration efforts? I wager the distro > installer guys will grumble at having to choose among duplicated RAID code > and formats. There has been some grumbling, but the benefits of using one linux-raid infrastructure for md-metadata and vendor metadata is appealing. mdadm-3.0 also makes a serious effort to be more agreeable with udev and incremental discovery. So hopefully this makes mdadm easier to handle in the installer. > 4) What is the plan for handling existing Intel RAID users (e.g. dmraid + > Intel RAID)? Has Intel been contacted about dmraid issues? What does Intel > think about this lovely user confusion shoved into their laps? The confusion was the other way round. We were faced with how to achieve long term feature parity of our raid solution across OS's and the community presented us with two directions DM and MD. The decision was made to support and maintain dmraid for existing deployments while basing future development on extending the MD stack, because it gave some feature advantages out of the gate. So, there is support for both and new development will focus on MD. > 5) Have the dmraid maintainer and DM folks been queried, given that you are > duplicating their functionality via Intel and DDF RAID formats? What was > their response, what issues were raised and resolved? There have been interludes, but not much in the way of discussion. Hopefully, this will be a starting point. Thanks, Dan [1] http://marc.info/?l=linux-raid&m=123300614013042&w=2 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-02 20:11 ` ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux Jeff Garzik 2009-06-02 22:58 ` Dan Williams @ 2009-06-03 3:56 ` Neil Brown 2009-06-03 13:01 ` Anton Altaparmakov ` (2 more replies) 1 sibling, 3 replies; 10+ messages in thread From: Neil Brown @ 2009-06-03 3:56 UTC (permalink / raw) To: Jeff Garzik Cc: linux-raid, LKML, linux-fsdevel, dm-devel, Arjan van de Ven, Alan Cox [dm-devel added for completeness] Hi Jeff, thanks for your thoughts. I agree this is a conversation worth having. On Tuesday June 2, jeff@garzik.org wrote: > Neil Brown wrote: > > The significant change which justifies the new major version number is > > that mdadm can now handle metadata updates entirely in userspace. > > This allows mdadm to support metadata formats that the kernel knows > > nothing about. > > > > Currently two such metadata formats are supported: > > - DDF - The SNIA standard format > > - Intel Matrix - The metadata used by recent Intel ICH controlers. > > This seems pretty awful from a support standpoint: dmraid has been the > sole provider of support for vendor-proprietary up until this point. And mdadm has been the sole provider of raid5 and raid6 (and, arguably, reliable raid1 - there was a thread recently about architectural issues in dm/raid1 that allowed data corruption). So either dmraid would have to support raid5, or mdadm would have to support IMSM. or both? > > Now Linux users -- and distro installers -- must choose between software > RAID stack "MD" and software RAID stack "DM". That choice is made _not_ > based on features, but on knowing the underlying RAID metadata format > that is required, and what features you need out of it. If you replace the word "required" by "supported", then the metadata format becomes a feature. And only md provides raid5/raid6. And only dm provides LVM. So I think there are plenty of "feature" issues between them. Maybe there are now more use-cases where the choice cannot be made based on features. I guess things like familiarity and track-record come in to play there. But choice is a crucial element of freedom. > > dmraid already supports > - Intel RAID format, touched by Intel as recently as 2007 > - DDF, the SNIA standard format > > This obviously generates some relevant questions... > > 1) Why? This obviously duplicates existing effort and code. The only > compelling reason I see is RAID5 support, which DM lacks IIRC -- but the > huge issue of user support and duplicated code remains. Yes, RAID5 (and RAID6) are big parts of the reason. RAID1 is not an immaterial part. But my initial motivation was that this was the direction I wanted the md code base to move in. It was previously locked to two internal metadata formats. I wanted to move the metadata support into userspace where I felt it belonged, and DDF was a good vehicle to drive that. Intel then approached me about adding IMSM support and I was happy to co-operate. > > 2) Adding container-like handling obviously moves MD in the direction of > DM. Does that imply someone will be looking at integrating the two > codebases, or will this begin to implement features also found in DM's > codebase? I wonder why you think "container-like" handling moves in the direction of DM. I see nothing in the DM that explicitly relates to this. There was something in MD (internal metadata support) which explicitly worked against it. I have since made that less of an issue. All the knowledge of containers is really in lvm2/dmraid and mdadm - the user-space tools (and I do think it is important to be aware of the distinction between the kernel side and the user side of each system). So this is really a case of md "seeing" the wisdom in that aspect of the design of "dm" and taking a similar approach - though with significantly different details. As for integrating the two code bases.... people have been suggesting that for years, but I suspect few of them have looked deeply at the practicalities. Apparently it was suggested at the recent "storage summit". However as the primary md and dm developers were absent, I have doubts about how truly well-informed that conversation could have been. I do have my own sketchy ideas about how unification could be achieved. It would involve creating a third "thing" and then migrating md and dm (and loop and nbd and drbd and ...) to mesh with that new model. But it is hard to make this a priority where there are more practically useful things to be done. It is worth reflecting again on the distinction between lvm2 or dmraid and dm, and between mdadm and md. lvm2 could conceivably use md. mdadm could conceivably use dm. I have certainly considered teaching mdadm to work with dm-multipath so that I could justifiably remove md/multipath without the risk of breaking someone's installation. But it isn't much of a priority. The dmraid developers might think that utilising md to provide some raid levels might be a good thing (now that I have shown it to be possible). I would be happy to support that to the extent of explaining how it can work and even refining interfaces if that proved to be necessary. Who knows - that could eventually lead to me being able to end-of-life mdadm and leave everyone using dmraid :-) Will md implement features found in dm's code base? For things like LVM, Multipath, crypt and snapshot : no, definitely not. For things like suspend/resume of incoming IO (so a device can be reconfigured), maybe. I recently added that so that I could effect raid5->raid6 conversions. I would much rather this was implemented in the block layer than in md or dm. I added it to md because that was the fastest path, and it allowed me to explore and come to understand the issues. I tried to arrange the implementation so that it could be moved up to the block layer without user-space noticing. Hopefully I will get around to attempting that before I forget all that I learnt. > > 3) What is the status of distro integration efforts? I wager the distro > installer guys will grumble at having to choose among duplicated RAID > code and formats. Some distros are shipping mdadm-3.0-pre releases, but I don't think any have seriously tried to integrate the DDF or IMSM support with installers or the boot process yet. Intel have engineers working to make sure such integration is possible, reliable, and relatively simple. Installers already understand lvm and mdadm for different use cases. Adding some new use cases that overlap should not be a big headache. They also already support ext3-vs-xfs, gnome-vs-kde etc. There is an issue of "if the drives appear to have DDF metadata, which tool shall I use". I am not well placed to give an objective answer to that. mdadm can easily be told to ignore such arrays unless explicitly requested to deal with them. A line like AUTO -ddf -imsm in mdadm.conf would ensure that auto-assembly and incremental assembly will ignore both DDF and IMSM. > > 4) What is the plan for handling existing Intel RAID users (e.g. dmraid > + Intel RAID)? Has Intel been contacted about dmraid issues? What does > Intel think about this lovely user confusion shoved into their laps? The above mentioned AUTO line can disable mdadm auto-management of such arrays. Maybe dmraid auto-management can be equally disabled. Distros might be well-advise to make the choice a configurable option. I cannot speak for Intel, except to acknowledge that their engineers have done most of the work to support IMSM is mdadm. I just provided the infrastructure and general consulting. > > 5) Have the dmraid maintainer and DM folks been queried, given that you > are duplicating their functionality via Intel and DDF RAID formats? > What was their response, what issues were raised and resolved? I haven't spoken to them, no (except for a couple of barely-related chats with Alasdair). By and large, they live in their little walled garden, and I/we live in ours. NeilBrown ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-03 3:56 ` Neil Brown @ 2009-06-03 13:01 ` Anton Altaparmakov 2009-06-03 14:42 ` Heinz Mauelshagen 2009-06-04 15:33 ` Larry Dickson 2 siblings, 0 replies; 10+ messages in thread From: Anton Altaparmakov @ 2009-06-03 13:01 UTC (permalink / raw) To: Neil Brown Cc: Jeff Garzik, linux-raid, LKML, linux-fsdevel, dm-devel, Arjan van de Ven, Alan Cox Hi Neil, Is there any documentation for the interface between mdadm and a metadata format "module" (if I can call it that way)? What I mean is: where would one start if one wanted to add a new metadata format to mdadm? Or is the only documentation the source code to mdadm? Thanks a lot in advance! Best regards, Anton -- Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @) Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK Linux NTFS maintainer, http://www.linux-ntfs.org/ ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-03 3:56 ` Neil Brown 2009-06-03 13:01 ` Anton Altaparmakov @ 2009-06-03 14:42 ` Heinz Mauelshagen 2009-06-03 17:26 ` [dm-devel] " Dan Williams 2009-06-08 23:32 ` [dm-devel] " Neil Brown 2009-06-04 15:33 ` Larry Dickson 2 siblings, 2 replies; 10+ messages in thread From: Heinz Mauelshagen @ 2009-06-03 14:42 UTC (permalink / raw) To: device-mapper development Cc: Jeff Garzik, LKML, linux-raid, linux-fsdevel, Alan Cox, Arjan van de Ven On Wed, 2009-06-03 at 13:56 +1000, Neil Brown wrote: > [dm-devel added for completeness] > > Hi Jeff, > thanks for your thoughts. > I agree this is a conversation worth having. > > On Tuesday June 2, jeff@garzik.org wrote: > > Neil Brown wrote: > > > > The significant change which justifies the new major version number is > > > that mdadm can now handle metadata updates entirely in userspace. > > > This allows mdadm to support metadata formats that the kernel knows > > > nothing about. > > > > > > Currently two such metadata formats are supported: > > > - DDF - The SNIA standard format > > > - Intel Matrix - The metadata used by recent Intel ICH controlers. > > > > This seems pretty awful from a support standpoint: dmraid has been the > > sole provider of support for vendor-proprietary up until this point. > > And mdadm has been the sole provider of raid5 and raid6 (and, > arguably, reliable raid1 - there was a thread recently about > architectural issues in dm/raid1 that allowed data corruption). > So either dmraid would have to support raid5, or mdadm would have to > support IMSM. or both? Hi, the dm-raid45 target patch has been adopted by various distros for that purpose since quite some time. It's providing RAID4 and RAID5 mappings but is not yet upstream. Support for IMSM 9.0 is being integrated. > > > > > Now Linux users -- and distro installers -- must choose between software > > RAID stack "MD" and software RAID stack "DM". That choice is made _not_ > > based on features, but on knowing the underlying RAID metadata format > > that is required, and what features you need out of it. > > If you replace the word "required" by "supported", then the metadata > format becomes a feature. And only md provides raid5/raid6. And only > dm provides LVM. So I think there are plenty of "feature" issues > between them. > Maybe there are now more use-cases where the choice cannot be made > based on features. I guess things like familiarity and track-record > come in to play there. But choice is a crucial element of freedom. > > > > > > dmraid already supports > > - Intel RAID format, touched by Intel as recently as 2007 Like mentioned, IMSM 9.0 being supported via an Intel contribution. > > - DDF, the SNIA standard format > > > > This obviously generates some relevant questions... > > > > 1) Why? This obviously duplicates existing effort and code. The only > > compelling reason I see is RAID5 support, which DM lacks IIRC -- but the > > huge issue of user support and duplicated code remains. > > Yes, RAID5 (and RAID6) are big parts of the reason. RAID1 is not an > immaterial part. > But my initial motivation was that this was the direction I wanted the > md code base to move in. It was previously locked to two internal > metadata formats. I wanted to move the metadata support into > userspace where I felt it belonged, and DDF was a good vehicle to > drive that. > Intel then approached me about adding IMSM support and I was happy to > co-operate. Like us for dmraid about IMSM 9.0 and other features. > > > > > 2) Adding container-like handling obviously moves MD in the direction of > > DM. Does that imply someone will be looking at integrating the two > > codebases, or will this begin to implement features also found in DM's > > codebase? > > I wonder why you think "container-like" handling moves in the > direction of DM. I see nothing in the DM that explicitly relates to > this. DM was initially designed to be container-style with respect to many areas and that included it to be metadata agnostic in order to handle any metadata formats in userspace. > There was something in MD (internal metadata support) which > explicitly worked against it. I have since made that less of an issue. > All the knowledge of containers is really in lvm2/dmraid and mdadm - the > user-space tools (and I do think it is important to be aware of the > distinction between the kernel side and the user side of each > system). > > So this is really a case of md "seeing" the wisdom in that aspect of > the design of "dm" and taking a similar approach - though with > significantly different details. Yes, you are working dm type features in since a while :-) > > As for integrating the two code bases.... people have been suggesting > that for years, but I suspect few of them have looked deeply at the > practicalities. Apparently it was suggested at the recent "storage > summit". However as the primary md and dm developers were absent, I > have doubts about how truly well-informed that conversation could have > been. Agreed, we'd need face-time and talk issues through in order to come up with any such plan for md+dm integration. > > I do have my own sketchy ideas about how unification could be > achieved. It would involve creating a third "thing" and then > migrating md and dm (and loop and nbd and drbd and ...) to mesh with > that new model. > But it is hard to make this a priority where there are more > practically useful things to be done. > > It is worth reflecting again on the distinction between lvm2 or dmraid > and dm, and between mdadm and md. > lvm2 could conceivably use md. With the exception of clustered storage. There's no e.g. clustered RAID1 in MD. > mdadm could conceivably use dm. > I have certainly considered teaching mdadm to work with dm-multipath > so that I could justifiably remove md/multipath without the risk of > breaking someone's installation. But it isn't much of a priority. > The dmraid developers might think that utilising md to provide some > raid levels might be a good thing (now that I have shown it to be > possible). I would be happy to support that to the extent of > explaining how it can work and even refining interfaces if that proved > to be necessary. Who knows - that could eventually lead to me being > able to end-of-life mdadm and leave everyone using dmraid :-) Your ':-)' is adaquate because dmraid just got features added to create/remove RAID sets and to handle spares recently with IMSM. Other metadata format handlers in dmraid have to be enhanced to support that functionality. > > Will md implement features found in dm's code base? > For things like LVM, Multipath, crypt and snapshot : no, definitely not. > For things like suspend/resume of incoming IO (so a device can be > reconfigured), maybe. I recently added that so that I could effect > raid5->raid6 conversions. I would much rather this was implemented in > the block layer than in md or dm. I added it to md because that was > the fastest path, and it allowed me to explore and come to understand > the issues. I tried to arrange the implementation so that it could be > moved up to the block layer without user-space noticing. Hopefully I > will get around to attempting that before I forget all that I learnt. > > > > > > 3) What is the status of distro integration efforts? I wager the distro > > installer guys will grumble at having to choose among duplicated RAID > > code and formats. > > Some distros are shipping mdadm-3.0-pre releases, but I don't think > any have seriously tried to integrate the DDF or IMSM support with > installers or the boot process yet. > Intel have engineers working to make sure such integration is > possible, reliable, and relatively simple. > > Installers already understand lvm and mdadm for different use cases. And dmraid. > Adding some new use cases that overlap should not be a big headache. > They also already support ext3-vs-xfs, gnome-vs-kde etc. > > There is an issue of "if the drives appear to have DDF metadata, which > tool shall I use". I am not well placed to give an objective answer > to that. > mdadm can easily be told to ignore such arrays unless explicitly > requested to deal with them. A line like > AUTO -ddf -imsm > in mdadm.conf would ensure that auto-assembly and incremental assembly > will ignore both DDF and IMSM. > > > > > 4) What is the plan for handling existing Intel RAID users (e.g. dmraid > > + Intel RAID)? Has Intel been contacted about dmraid issues? What does > > Intel think about this lovely user confusion shoved into their laps? > > The above mentioned AUTO line can disable mdadm auto-management of > such arrays. Maybe dmraid auto-management can be equally disabled. > dmraid already supports that since ever but goes by the different approach to allow the metadata to be selected with the -f option, hence ignoring any RAID sets with other metadata. > Distros might be well-advise to make the choice a configurable > option. > > I cannot speak for Intel, except to acknowledge that their engineers > have done most of the work to support IMSM is mdadm. I just provided > the infrastructure and general consulting. > > > > > 5) Have the dmraid maintainer and DM folks been queried, given that you > > are duplicating their functionality via Intel and DDF RAID formats? > > What was their response, what issues were raised and resolved? > > I haven't spoken to them, no (except for a couple of barely-related > chats with Alasdair). > By and large, they live in their little walled garden, and I/we live > in ours. Maybe we are about to change that? ;-) Heinz > > NeilBrown > > -- > dm-devel mailing list > dm-devel@redhat.com > https://www.redhat.com/mailman/listinfo/dm-devel ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [dm-devel] Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-03 14:42 ` Heinz Mauelshagen @ 2009-06-03 17:26 ` Dan Williams 2009-06-04 16:38 ` Heinz Mauelshagen 2009-06-08 23:32 ` [dm-devel] " Neil Brown 1 sibling, 1 reply; 10+ messages in thread From: Dan Williams @ 2009-06-03 17:26 UTC (permalink / raw) To: heinzm, device-mapper development Cc: Jeff Garzik, LKML, linux-raid, linux-fsdevel, Alan Cox, Arjan van de Ven, Ed Ciechanowski, Jacek Danecki On Wed, Jun 3, 2009 at 7:42 AM, Heinz Mauelshagen <heinzm@redhat.com> wrote: > On Wed, 2009-06-03 at 13:56 +1000, Neil Brown wrote: >> As for integrating the two code bases.... people have been suggesting >> that for years, but I suspect few of them have looked deeply at the >> practicalities. Apparently it was suggested at the recent "storage >> summit". However as the primary md and dm developers were absent, I >> have doubts about how truly well-informed that conversation could have >> been. > > Agreed, we'd need face-time and talk issues through in order to come up > with any such plan for md+dm integration. > What are your general impressions of dmraid using md kernel infrastructure for raid level support? Thanks, Dan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-03 17:26 ` [dm-devel] " Dan Williams @ 2009-06-04 16:38 ` Heinz Mauelshagen 0 siblings, 0 replies; 10+ messages in thread From: Heinz Mauelshagen @ 2009-06-04 16:38 UTC (permalink / raw) To: Dan Williams Cc: Jeff Garzik, Jacek Danecki, LKML, Ed Ciechanowski, linux-raid, device-mapper development, linux-fsdevel, Alan Cox, Arjan van de Ven On Wed, 2009-06-03 at 10:26 -0700, Dan Williams wrote: > On Wed, Jun 3, 2009 at 7:42 AM, Heinz Mauelshagen <heinzm@redhat.com> wrote: > > On Wed, 2009-06-03 at 13:56 +1000, Neil Brown wrote: > >> As for integrating the two code bases.... people have been suggesting > >> that for years, but I suspect few of them have looked deeply at the > >> practicalities. Apparently it was suggested at the recent "storage > >> summit". However as the primary md and dm developers were absent, I > >> have doubts about how truly well-informed that conversation could have > >> been. > > > > Agreed, we'd need face-time and talk issues through in order to come up > > with any such plan for md+dm integration. > > > > What are your general impressions of dmraid using md kernel > infrastructure for raid level support? At the time of the dmraid project start, we already had libdevmapper which was suitable to handle in-kernel device manipulation with no adequate on the MD side so it was the appropriate interface to use. Cheers, Heinz > > Thanks, > Dan ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [dm-devel] Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-03 14:42 ` Heinz Mauelshagen 2009-06-03 17:26 ` [dm-devel] " Dan Williams @ 2009-06-08 23:32 ` Neil Brown 2009-06-09 16:29 ` Heinz Mauelshagen 1 sibling, 1 reply; 10+ messages in thread From: Neil Brown @ 2009-06-08 23:32 UTC (permalink / raw) To: heinzm, device-mapper development Cc: Jeff Garzik, LKML, linux-raid, linux-fsdevel, Alan Cox, Arjan van de Ven On Wednesday June 3, heinzm@redhat.com wrote: > > > > I haven't spoken to them, no (except for a couple of barely-related > > chats with Alasdair). > > By and large, they live in their little walled garden, and I/we live > > in ours. > > Maybe we are about to change that? ;-) Maybe ... what should we talk about? Two areas where I think we might be able to have productive discussion: 1/ Making md personalities available as dm targets. In one sense this is trivial as an block device can be a DM target, and any md personality can be a block device. However it might be more attractive if the md personality responded to dm ioctls. Considering specifically raid5, some aspects of plugging md/raid5 underneath dm would be trivial - e.g. assembling the array at the start. However others are not so straight forward. In particular, when a drive fails in a raid5, you need to update the metadata before allowing any writes which depend on that drive to complete. Given that metadata is managed in user-space, this means signalling user-space and waiting for a response. md does this via a file in sysfs. I cannot see any similar mechanism in dm, but I haven't looked very hard. Would it be useful to pursue this do you think? 2/ It might be useful to have a common view how virtual devices in general should be managed in Linux. Then we could independently migrated md and dm towards this goal. I imagine a block-layer level function which allows a blank virtual device to be created, with an arbitrary major/minor allocated. e.g. echo foo > /sys/block/.new causes /sys/devices/virtual/block/foo/ to be created. Then a similar mechanism associates that with a particular driver. That causes more attributes to appear in ../block/foo/ which can be used to flesh out the details of the device. There would be library code that a driver could use to: - accept subordinate devices - manage the state of those devices - maintain a write-intent bitmap etc. There would also need to be a block-layer function to suspend/resume or similar so that a block device can be changed underneath a filesystem. We currently have three structures for a block device: struct block_device -> struct gendisk -> struct request_queue I imagine allow either the "struct gendisk" or the "struct request_queue" to be swapped between two "struct block_device". I'm not sure which, and the rest of the details are even more fuzzy. That sort of infrastructure would allow interesting migrations without being limited to "just with dm" or "just within md". Thoughts? NeilBrown ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-08 23:32 ` [dm-devel] " Neil Brown @ 2009-06-09 16:29 ` Heinz Mauelshagen 0 siblings, 0 replies; 10+ messages in thread From: Heinz Mauelshagen @ 2009-06-09 16:29 UTC (permalink / raw) To: device-mapper development Cc: Jeff Garzik, LKML, linux-raid, linux-fsdevel, Alan Cox, Arjan van de Ven On Tue, 2009-06-09 at 09:32 +1000, Neil Brown wrote: > On Wednesday June 3, heinzm@redhat.com wrote: > > > > > > I haven't spoken to them, no (except for a couple of barely-related > > > chats with Alasdair). > > > By and large, they live in their little walled garden, and I/we live > > > in ours. > > > > Maybe we are about to change that? ;-) > > Maybe ... what should we talk about? > > Two areas where I think we might be able to have productive > discussion: > > 1/ Making md personalities available as dm targets. > In one sense this is trivial as an block device can be a DM > target, and any md personality can be a block device. Of course one could stack a linear target on any MD personality and live with the minor overhead in the io path. The overhead to handle such stacking on the tool side of things is not negligible though, hence it's a better option to have native dm targets for these mappings. > However it might be more attractive if the md personality > responded to dm ioctls. Indeed, we need the full interface to be covered in order to stay homogeneous. > Considering specifically raid5, some aspects of plugging > md/raid5 underneath dm would be trivial - e.g. assembling the > array at the start. > However others are not so straight forward. > In particular, when a drive fails in a raid5, you need to update > the metadata before allowing any writes which depend on that drive > to complete. Given that metadata is managed in user-space, this > means signalling user-space and waiting for a response. > md does this via a file in sysfs. I cannot see any similar > mechanism in dm, but I haven't looked very hard. We use events passed to a uspace daemon via an ioctl interface and our suspend/resume mechanism to ensure such metadata updates. > > Would it be useful to pursue this do you think? I looked at the MD personality back in time when I was searching for an option to support RAID5 in dm but, like you similarly noted above, didn't find a simple way to wrap it into a dm target so the answer *was* no. That's why I picked some code (e.g. the RAID adressing) and implemented a target of my own. > > > 2/ It might be useful to have a common view how virtual devices in > general should be managed in Linux. Then we could independently > migrated md and dm towards this goal. > > I imagine a block-layer level function which allows a blank > virtual device to be created, with an arbitrary major/minor > allocated. > e.g. > echo foo > /sys/block/.new > causes > /sys/devices/virtual/block/foo/ > to be created. > Then a similar mechanism associates that with a particular driver. > That causes more attributes to appear in ../block/foo/ which > can be used to flesh out the details of the device. > > There would be library code that a driver could use to: > - accept subordinate devices > - manage the state of those devices > - maintain a write-intent bitmap > etc. Yes, and such library can be filled with ported dm/md and other code. > > There would also need to be a block-layer function to > suspend/resume or similar so that a block device can be changed > underneath a filesystem. Yes, consolidating such functionality in a central place is the proper design but we still need an interface into any block driver which is initiating io on its own behalf (e.g. mirror resynchronization) in order to ensure, that such io gets suspended/resumed consistently > > We currently have three structures for a block device: > struct block_device -> struct gendisk -> struct request_queue > > I imagine allow either the "struct gendisk" or the "struct > request_queue" to be swapped between two "struct block_device". > I'm not sure which, and the rest of the details are even more > fuzzy. > > That sort of infrastructure would allow interesting migrations > without being limited to "just with dm" or "just within md". Or just with other virtual drivers such as drbd. Hard to imagine issues at the detailed spec level before they are fleshed out but this sounds like a good idea to start with. Heinz > > Thoughts? > > NeilBrown > > -- > dm-devel mailing list > dm-devel@redhat.com > https://www.redhat.com/mailman/listinfo/dm-devel ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: Re: ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux 2009-06-03 3:56 ` Neil Brown 2009-06-03 13:01 ` Anton Altaparmakov 2009-06-03 14:42 ` Heinz Mauelshagen @ 2009-06-04 15:33 ` Larry Dickson 2 siblings, 0 replies; 10+ messages in thread From: Larry Dickson @ 2009-06-04 15:33 UTC (permalink / raw) To: device-mapper development Cc: Jeff Garzik, LKML, linux-raid, linux-fsdevel, Alan Cox, Arjan van de Ven [-- Attachment #1.1: Type: text/plain, Size: 1000 bytes --] Hi all, As a user of both dm (in lvm) and md, I am not reassured by the "turf war" flavor coming from the dm side. The idea that all functions should be glooped together in one monster program, whether dm or the Microsoft operating system, is not an automatic + in my opinion. The massive patch activity that I see in dm-devel could be an indication of function overcentralization leading to design risk, just as in Microsoft development. A minor technical note follows. > For things like suspend/resume of incoming IO (so a device can be > reconfigured), maybe. I recently added that so that I could effect > raid5->raid6 conversions. Suspend is not necessary, only barriers, as long as you define a hybrid raid5/raid6 array via a moving watermark. Only those IOs that hit in the neighborhood of the watermark are affected. Larry Dickson Cutting Edge Networked Storage > NeilBrown > > -- > dm-devel mailing list > dm-devel@redhat.com > https://www.redhat.com/mailman/listinfo/dm-devel > [-- Attachment #1.2: Type: text/html, Size: 1516 bytes --] [-- Attachment #2: Type: text/plain, Size: 0 bytes --] ^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2009-06-09 16:29 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
[not found] <18980.48553.328662.80987@notabene.brown>
2009-06-02 20:11 ` ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux Jeff Garzik
2009-06-02 22:58 ` Dan Williams
2009-06-03 3:56 ` Neil Brown
2009-06-03 13:01 ` Anton Altaparmakov
2009-06-03 14:42 ` Heinz Mauelshagen
2009-06-03 17:26 ` [dm-devel] " Dan Williams
2009-06-04 16:38 ` Heinz Mauelshagen
2009-06-08 23:32 ` [dm-devel] " Neil Brown
2009-06-09 16:29 ` Heinz Mauelshagen
2009-06-04 15:33 ` Larry Dickson
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).