[linux-lvm] Progress on LVM2 snapshots

[linux-lvm] Progress on LVM2 snapshots

[Mukund]

Dear all,

	Please can anyone -authoritative- tell me about the current state of
snapshots support in LVM2? It was broken a while ago and I want to know
if it has been fixed now. I am the author of a storage management
project (www.openfiler.org), and we are currently stuck with LVM1 (and
the RHEL3 2.4 kernel and hence smaller device sizes) due to non-working
snapshots. Can LVM2 snapshots now be created and used reliably?

				Mukund

Re: [linux-lvm] Progress on LVM2 snapshots

[Ming Zhang]

yes, i believe now a lot of people has this question now.

is this question

1) very hard to solve technically. or
2) not so easy but doable, just no time and human resource?

thanks!

Ming


On Mon, 2005-06-20 at 12:45 +0100, Mukund wrote:
> Dear all,
> 
> 	Please can anyone -authoritative- tell me about the current state of
> snapshots support in LVM2? It was broken a while ago and I want to know
> if it has been fixed now. I am the author of a storage management
> project (www.openfiler.org), and we are currently stuck with LVM1 (and
> the RHEL3 2.4 kernel and hence smaller device sizes) due to non-working
> snapshots. Can LVM2 snapshots now be created and used reliably?
> 
> 				Mukund
> 
> 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] Progress on LVM2 snapshots

[Jonathan E Brassow]

#2

I know agk had some plans for cleaning up single machine snapshots, but 
he is backed up behind reviewing/working on multipath and mirroring (in 
addition to traveling all over for conferences:).

  brassow

On Jul 28, 2005, at 12:44 PM, Ming Zhang wrote:

> yes, i believe now a lot of people has this question now.
>
> is this question
>
> 1) very hard to solve technically. or
> 2) not so easy but doable, just no time and human resource?
>
> thanks!
>
> Ming
>
>
> On Mon, 2005-06-20 at 12:45 +0100, Mukund wrote:
>> Dear all,
>>
>> 	Please can anyone -authoritative- tell me about the current state of
>> snapshots support in LVM2? It was broken a while ago and I want to 
>> know
>> if it has been fixed now. I am the author of a storage management
>> project (www.openfiler.org), and we are currently stuck with LVM1 (and
>> the RHEL3 2.4 kernel and hence smaller device sizes) due to 
>> non-working
>> snapshots. Can LVM2 snapshots now be created and used reliably?
>>
>> 				Mukund
>>
>>
>>
>> _______________________________________________
>> linux-lvm mailing list
>> linux-lvm@redhat.com
>> https://www.redhat.com/mailman/listinfo/linux-lvm
>> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>

Re: [linux-lvm] Progress on LVM2 snapshots

[Ming Zhang]

Thanks a lot for this information.

Is there anything external people like us can do to speed up this? There
are many people waiting for this snapshot feature since it is so useful
and essential. frankly, i know there are plan to replace md with dm, but
since md is already stable and this snapshot is very unstable, why not
do this first? :P

Ming

On Thu, 2005-07-28 at 15:06 -0500, Jonathan E Brassow wrote:
> #2
> 
> I know agk had some plans for cleaning up single machine snapshots, but 
> he is backed up behind reviewing/working on multipath and mirroring (in 
> addition to traveling all over for conferences:).
> 
>   brassow
> 
> On Jul 28, 2005, at 12:44 PM, Ming Zhang wrote:
> 
> > yes, i believe now a lot of people has this question now.
> >
> > is this question
> >
> > 1) very hard to solve technically. or
> > 2) not so easy but doable, just no time and human resource?
> >
> > thanks!
> >
> > Ming
> >
> >
> > On Mon, 2005-06-20 at 12:45 +0100, Mukund wrote:
> >> Dear all,
> >>
> >> 	Please can anyone -authoritative- tell me about the current state of
> >> snapshots support in LVM2? It was broken a while ago and I want to 
> >> know
> >> if it has been fixed now. I am the author of a storage management
> >> project (www.openfiler.org), and we are currently stuck with LVM1 (and
> >> the RHEL3 2.4 kernel and hence smaller device sizes) due to 
> >> non-working
> >> snapshots. Can LVM2 snapshots now be created and used reliably?
> >>
> >> 				Mukund
> >>
> >>
> >>
> >> _______________________________________________
> >> linux-lvm mailing list
> >> linux-lvm@redhat.com
> >> https://www.redhat.com/mailman/listinfo/linux-lvm
> >> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> >
> > _______________________________________________
> > linux-lvm mailing list
> > linux-lvm@redhat.com
> > https://www.redhat.com/mailman/listinfo/linux-lvm
> > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> >
> 

Re: [linux-lvm] Progress on LVM2 snapshots

[Jonathan E Brassow]

On Jul 28, 2005, at 3:26 PM, Ming Zhang wrote:

> Thanks a lot for this information.
np

> Is there anything external people like us can do to speed up this?

1) File detailed bug reports
2) complain on this list
3) submit patches

>  There
> are many people waiting for this snapshot feature since it is so useful
> and essential. frankly, i know there are plan to replace md with dm, 
> but
> since md is already stable and this snapshot is very unstable, why not
> do this first? :P

The squeaky wheel gets the grease.  Right now, multipath, [cluster] 
mirroring have been getting all the attention at the expense of single 
machine snap-shot.  Hopefully, we can get snapshots soon.

  brassow

Re: [linux-lvm] Progress on LVM2 snapshots

[Ming Zhang]

On Thu, 2005-07-28 at 15:45 -0500, Jonathan E Brassow wrote:
> On Jul 28, 2005, at 3:26 PM, Ming Zhang wrote:
> 
> > Thanks a lot for this information.
> np
> 
> > Is there anything external people like us can do to speed up this?
> 
> 1) File detailed bug reports
> 2) complain on this list
> 3) submit patches
> 
> >  There
> > are many people waiting for this snapshot feature since it is so useful
> > and essential. frankly, i know there are plan to replace md with dm, 
> > but
> > since md is already stable and this snapshot is very unstable, why not
> > do this first? :P
> 
> The squeaky wheel gets the grease.  Right now, multipath, [cluster] 
> mirroring have been getting all the attention at the expense of single 
> machine snap-shot.  Hopefully, we can get snapshots soon.
> 

:P u are rite. this is the truth. when both are important, loud voice
gains.


>   brassow
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] Progress on LVM2 snapshots

[Alasdair G Kergon]

On Thu, Jul 28, 2005 at 01:44:00PM -0400, Ming Zhang wrote:
> 1) very hard to solve technically. or
> 2) not so easy but doable, just no time and human resource?
 
The hardest part of the fix involves changing the sequence of 
device-mapper ioctls that LVM2 uses, and that's a couple of weeks' 
development work, now pencilled into the RHEL4 Update 3 timescale.

In the meantime, you can apply the snapshot patches in the -udm
tree and use 'dmsetup' manually to activate and deactivate snapshots
when lvm2 fails.

Patches 8 and 9 at:
  ftp://sources.redhat.com/pub/dm/patches/2.6-unstable/2.6.12-rc2/2.6.12-rc2-udm1/
(Further patches are needed, but those two plus correct dmsetup use
should avoid machine lockups.)

Alasdair
-- 
agk@redhat.com

Re: [linux-lvm] Progress on LVM2 snapshots

[Ming Zhang]

thanks!

so when is the RHEL4 Update 3 timescale? :)


will try the patches u mentioned.


ming


On Fri, 2005-07-29 at 21:47 +0100, Alasdair G Kergon wrote:
> On Thu, Jul 28, 2005 at 01:44:00PM -0400, Ming Zhang wrote:
> > 1) very hard to solve technically. or
> > 2) not so easy but doable, just no time and human resource?
>  
> The hardest part of the fix involves changing the sequence of 
> device-mapper ioctls that LVM2 uses, and that's a couple of weeks' 
> development work, now pencilled into the RHEL4 Update 3 timescale.
> 
> In the meantime, you can apply the snapshot patches in the -udm
> tree and use 'dmsetup' manually to activate and deactivate snapshots
> when lvm2 fails.
> 
> Patches 8 and 9 at:
>   ftp://sources.redhat.com/pub/dm/patches/2.6-unstable/2.6.12-rc2/2.6.12-rc2-udm1/
> (Further patches are needed, but those two plus correct dmsetup use
> should avoid machine lockups.)
> 
> Alasdair