Mdadm, udev and fakeraid?

Mdadm, udev and fakeraid?

[Seblu]

Hello,

In the following commit, udev rules load isw_raid (fakeraid). From my
test, this doesnt work. I have to call dmraid to have something
working.
http://neil.brown.name/git?p=mdadm;a=commit;h=475a01b8bce8575dd1b2ab6495e65e854702ac0e

isw_raid is only fakeraid devices? mdadm is able to mount fakeraid partition?

Regards,

-- 
Sébastien Luttringer
www.seblu.net
--
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

Re: Mdadm, udev and fakeraid?

[NeilBrown]

On Sun, 3 Apr 2011 18:03:50 +0200 Seblu <seblu@seblu.net> wrote:

> Hello,
> 
> In the following commit, udev rules load isw_raid (fakeraid). From my
> test, this doesnt work. I have to call dmraid to have something
> working.
> http://neil.brown.name/git?p=mdadm;a=commit;h=475a01b8bce8575dd1b2ab6495e65e854702ac0e
> 
> isw_raid is only fakeraid devices? mdadm is able to mount fakeraid partition?
> 

I'm sorry but I cannot parse those questions successfully so I'm not sure
what you are asking.


Both dmraid and mdadm can manage some 'fakeraid' arrays.  dmraid supports a
wider variety.  mdadm supports raid1 and raid5 more completely than dmraid
does.

Both should support isw to some degree.
Intel are currently working with mdadm to make it provide full support for
"IMSM" (Intel Matrix Storage Manager).  I don't know the exact relationship
between 'isw' and 'IMSM' - maybe they are different names for the same thing.

If mdadm doesn't work for your isw arrays, and you want it to, then I suggest
you report details about what is, or is not, happening.

Useful information would include:

 mdadm --examine /dev/DEVICE
for each device in the array.
Also the output of

 mdadm --incremental --verbose /dev/DEVICE
for each device in turn.  This should incrementally assemble the array from
all those components.

NeilBrown

Re: Mdadm, udev and fakeraid?

[Seblu]

On Tue, Apr 5, 2011 at 8:20 AM, NeilBrown <neilb@suse.de> wrote:
> On Sun, 3 Apr 2011 18:03:50 +0200 Seblu <seblu@seblu.net> wrote:
>
>> Hello,
>>
>> In the following commit, udev rules load isw_raid (fakeraid). From my
>> test, this doesnt work. I have to call dmraid to have something
>> working.
>> http://neil.brown.name/git?p=mdadm;a=commit;h=475a01b8bce8575dd1b2ab6495e65e854702ac0e
>>
>> isw_raid is only fakeraid devices? mdadm is able to mount fakeraid partition?
>>
>
> I'm sorry but I cannot parse those questions successfully so I'm not sure
> what you are asking.

Hello Neil,

in my previous mail, i used word fakeraid about raid created with
dmraid and i used softraid about raid created with mdadm. it was not
clear.

So my question was about compatibily. Raids created by dmraid can be
assembled with mdadm and vice versa?

> Both dmraid and mdadm can manage some 'fakeraid' arrays.  dmraid supports a
> wider variety.  mdadm supports raid1 and raid5 more completely than dmraid
> does.
mdadm -> create soft raid for linux  (now there is new format: ddf and imsm) ?
dmraid -> create soft raid from industry raid card format  ?

> Both should support isw to some degree.
> Intel are currently working with mdadm to make it provide full support for
> "IMSM" (Intel Matrix Storage Manager).  I don't know the exact relationship
> between 'isw' and 'IMSM' - maybe they are different names for the same thing.
ok

> If mdadm doesn't work for your isw arrays, and you want it to, then I suggest
> you report details about what is, or is not, happening.
My purpose is to improve archlinux startup detection of fakeraids
(mdadm + dmraid).

With mdadm everything works correctly without call to "mdadm -As"
With dmraid, no raid is created by udev rules, so we need to run
"dmraid -i -ay" at startup.

To test this kind of raid, i created a dmraid array in a vm. This
created me a /dev/mapper/isw_bfbjdbadhb_testF device.
call blkid on a disk member of this raid tell me this:
/dev/sde: TYPE="isw_raid_member"
and on "mdadm" created raid:
/dev/sdd: UUID="a974b525-993a-1481-f860-6471f3f120e1"
UUID_SUB="eb22aee2-b2ee-e56d-1008-44d52c63564d" LABEL="archipel:0"
TYPE="linux_raid_member"

This misled me because mdadm udev rules uses the output of blkid to
mount raids which have type "isw_raid_member".
What disturbs me is that mdadm cannot mount raid created by dmraid
with type isw_raid_member.

About outputs:
mdadm -I --verbose /dev/sde
mdadm: no RAID superblock on /dev/sde.

# mdadm --examine /dev/sde
/dev/sde:
          Magic : Intel Raid ISM Cfg Sig.
        Version : 1.1.00
    Orig Family : 5a8ed623
         Family : 5a8ed623
     Generation : 00000000
           UUID : ae2e9cd8:7fa43248:47c694a1:24990cbc
       Checksum : c23b6c88 correct
    MPB Sectors : 1
          Disks : 2
   RAID Devices : 1

  Disk00 Serial : 66faec8-9f5b237d
          State : active
             Id : 00040000
    Usable Size : 1019486 (497.88 MiB 521.98 MB)

[testF]:
           UUID : 6640a4cc:5faa1ce3:c1bff2b3:1093ca7d
     RAID Level : 1
        Members : 2
          Slots : [UU]
    Failed disk : none
      This Slot : 0
     Array Size : 1014446 (495.42 MiB 519.40 MB)
   Per Dev Size : 1014792 (495.59 MiB 519.57 MB)
  Sector Offset : 0
    Num Stripes : 3963
     Chunk Size : 64 KiB
       Reserved : 0
  Migrate State : idle
      Map State : normal
    Dirty State : clean

  Disk01 Serial : 0b540c6-4e527908
          State : active
             Id : 00050000
    Usable Size : 1019486 (497.88 MiB 521.98 MB)


Do not you think that dmraid should also ship an udev rules file to
mount the raid which can handle?

Regards,

-- 
Sébastien Luttringer
www.seblu.net
--
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

Re: Mdadm, udev and fakeraid?

[Luca Berra]

On Fri, Apr 15, 2011 at 04:15:50PM +0200, Seblu wrote:
>To test this kind of raid, i created a dmraid array in a vm. This
                                                      ^^^^^^^^^^
>created me a /dev/mapper/isw_bfbjdbadhb_testF device.
....

>About outputs:
>mdadm -I --verbose /dev/sde
>mdadm: no RAID superblock on /dev/sde.

mdadm checks if there is an Intel Matrix controller before checking for
intel raid superblocks. On your vm you don't have an intel raid
controller.
override with environment variable IMSM_NO_PLATFORM

....
>Do not you think that dmraid should also ship an udev rules file to
>mount the raid which can handle?
NO

-- 
Luca Berra -- bluca@comedia.it

Re: Mdadm, udev and fakeraid?

[NeilBrown]

On Fri, 15 Apr 2011 16:15:50 +0200 Seblu <seblu@seblu.net> wrote:

> On Tue, Apr 5, 2011 at 8:20 AM, NeilBrown <neilb@suse.de> wrote:
> > On Sun, 3 Apr 2011 18:03:50 +0200 Seblu <seblu@seblu.net> wrote:
> >
> >> Hello,
> >>
> >> In the following commit, udev rules load isw_raid (fakeraid). From my
> >> test, this doesnt work. I have to call dmraid to have something
> >> working.
> >> http://neil.brown.name/git?p=mdadm;a=commit;h=475a01b8bce8575dd1b2ab6495e65e854702ac0e
> >>
> >> isw_raid is only fakeraid devices? mdadm is able to mount fakeraid partition?
> >>
> >
> > I'm sorry but I cannot parse those questions successfully so I'm not sure
> > what you are asking.
> 
> Hello Neil,
> 
> in my previous mail, i used word fakeraid about raid created with
> dmraid and i used softraid about raid created with mdadm. it was not
> clear.
> 
> So my question was about compatibily. Raids created by dmraid can be
> assembled with mdadm and vice versa?
> 
> > Both dmraid and mdadm can manage some 'fakeraid' arrays.  dmraid supports a
> > wider variety.  mdadm supports raid1 and raid5 more completely than dmraid
> > does.
> mdadm -> create soft raid for linux  (now there is new format: ddf and imsm) ?
> dmraid -> create soft raid from industry raid card format  ?

No, it isn't that simple.

dmraid uses the 'dm' kernel module.  mdadm uses the 'md' kernel module.

As such dmraid doesn't support RAID5 (yet) and doesn't support RAID1 very
well.
mdadm supports both of these well, but doesn't support the same range of
"industry raid card formats".

There is a growing amount of overlap.

> 
> > Both should support isw to some degree.
> > Intel are currently working with mdadm to make it provide full support for
> > "IMSM" (Intel Matrix Storage Manager).  I don't know the exact relationship
> > between 'isw' and 'IMSM' - maybe they are different names for the same thing.
> ok
> 
> > If mdadm doesn't work for your isw arrays, and you want it to, then I suggest
> > you report details about what is, or is not, happening.
> My purpose is to improve archlinux startup detection of fakeraids
> (mdadm + dmraid).
> 
> With mdadm everything works correctly without call to "mdadm -As"
> With dmraid, no raid is created by udev rules, so we need to run
> "dmraid -i -ay" at startup.
> 
> To test this kind of raid, i created a dmraid array in a vm. This
> created me a /dev/mapper/isw_bfbjdbadhb_testF device.
> call blkid on a disk member of this raid tell me this:
> /dev/sde: TYPE="isw_raid_member"
> and on "mdadm" created raid:
> /dev/sdd: UUID="a974b525-993a-1481-f860-6471f3f120e1"
> UUID_SUB="eb22aee2-b2ee-e56d-1008-44d52c63564d" LABEL="archipel:0"
> TYPE="linux_raid_member"
> 
> This misled me because mdadm udev rules uses the output of blkid to
> mount raids which have type "isw_raid_member".
> What disturbs me is that mdadm cannot mount raid created by dmraid
> with type isw_raid_member.
> 
> About outputs:
> mdadm -I --verbose /dev/sde
> mdadm: no RAID superblock on /dev/sde.

As has been mentioned elsewhere, mdadm only recognised IMSM arrays on
machines with IMSM hardware.  I'm not entirely happy about this and may well
change it.


> 
> # mdadm --examine /dev/sde
> /dev/sde:
>           Magic : Intel Raid ISM Cfg Sig.
>         Version : 1.1.00
>     Orig Family : 5a8ed623
>          Family : 5a8ed623
>      Generation : 00000000
>            UUID : ae2e9cd8:7fa43248:47c694a1:24990cbc
>        Checksum : c23b6c88 correct
>     MPB Sectors : 1
>           Disks : 2
>    RAID Devices : 1
> 
>   Disk00 Serial : 66faec8-9f5b237d
>           State : active
>              Id : 00040000
>     Usable Size : 1019486 (497.88 MiB 521.98 MB)
> 
> [testF]:
>            UUID : 6640a4cc:5faa1ce3:c1bff2b3:1093ca7d
>      RAID Level : 1
>         Members : 2
>           Slots : [UU]
>     Failed disk : none
>       This Slot : 0
>      Array Size : 1014446 (495.42 MiB 519.40 MB)
>    Per Dev Size : 1014792 (495.59 MiB 519.57 MB)
>   Sector Offset : 0
>     Num Stripes : 3963
>      Chunk Size : 64 KiB
>        Reserved : 0
>   Migrate State : idle
>       Map State : normal
>     Dirty State : clean
> 
>   Disk01 Serial : 0b540c6-4e527908
>           State : active
>              Id : 00050000
>     Usable Size : 1019486 (497.88 MiB 521.98 MB)
> 
> 
> Do not you think that dmraid should also ship an udev rules file to
> mount the raid which can handle?

I have no opinion about what dmraid should do.  I have enough trouble working
out what mdadm should do :-)

NeilBrown


> 
> Regards,
> 

--
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

Re: Mdadm, udev and fakeraid?

[Seblu]

On Mon, Apr 18, 2011 at 2:38 AM, NeilBrown <neilb@suse.de> wrote:
> On Fri, 15 Apr 2011 16:15:50 +0200 Seblu <seblu@seblu.net> wrote:
>
>> On Tue, Apr 5, 2011 at 8:20 AM, NeilBrown <neilb@suse.de> wrote:
>> > On Sun, 3 Apr 2011 18:03:50 +0200 Seblu <seblu@seblu.net> wrote:
>> >
>> >> Hello,
>> >>
>> >> In the following commit, udev rules load isw_raid (fakeraid). From my
>> >> test, this doesnt work. I have to call dmraid to have something
>> >> working.
>> >> http://neil.brown.name/git?p=mdadm;a=commit;h=475a01b8bce8575dd1b2ab6495e65e854702ac0e
>> >>
>> >> isw_raid is only fakeraid devices? mdadm is able to mount fakeraid partition?
>> >>
>> >
>> > I'm sorry but I cannot parse those questions successfully so I'm not sure
>> > what you are asking.
>>
>> Hello Neil,
>>
>> in my previous mail, i used word fakeraid about raid created with
>> dmraid and i used softraid about raid created with mdadm. it was not
>> clear.
>>
>> So my question was about compatibily. Raids created by dmraid can be
>> assembled with mdadm and vice versa?
>>
>> > Both dmraid and mdadm can manage some 'fakeraid' arrays.  dmraid supports a
>> > wider variety.  mdadm supports raid1 and raid5 more completely than dmraid
>> > does.
>> mdadm -> create soft raid for linux  (now there is new format: ddf and imsm) ?
>> dmraid -> create soft raid from industry raid card format  ?
>
> No, it isn't that simple.
>
> dmraid uses the 'dm' kernel module.  mdadm uses the 'md' kernel module.
>
> As such dmraid doesn't support RAID5 (yet) and doesn't support RAID1 very
> well.
> mdadm supports both of these well, but doesn't support the same range of
> "industry raid card formats".
>
> There is a growing amount of overlap.
>
>>
>> > Both should support isw to some degree.
>> > Intel are currently working with mdadm to make it provide full support for
>> > "IMSM" (Intel Matrix Storage Manager).  I don't know the exact relationship
>> > between 'isw' and 'IMSM' - maybe they are different names for the same thing.
>> ok
>>
>> > If mdadm doesn't work for your isw arrays, and you want it to, then I suggest
>> > you report details about what is, or is not, happening.
>> My purpose is to improve archlinux startup detection of fakeraids
>> (mdadm + dmraid).
>>
>> With mdadm everything works correctly without call to "mdadm -As"
>> With dmraid, no raid is created by udev rules, so we need to run
>> "dmraid -i -ay" at startup.
>>
>> To test this kind of raid, i created a dmraid array in a vm. This
>> created me a /dev/mapper/isw_bfbjdbadhb_testF device.
>> call blkid on a disk member of this raid tell me this:
>> /dev/sde: TYPE="isw_raid_member"
>> and on "mdadm" created raid:
>> /dev/sdd: UUID="a974b525-993a-1481-f860-6471f3f120e1"
>> UUID_SUB="eb22aee2-b2ee-e56d-1008-44d52c63564d" LABEL="archipel:0"
>> TYPE="linux_raid_member"
>>
>> This misled me because mdadm udev rules uses the output of blkid to
>> mount raids which have type "isw_raid_member".
>> What disturbs me is that mdadm cannot mount raid created by dmraid
>> with type isw_raid_member.
>>
>> About outputs:
>> mdadm -I --verbose /dev/sde
>> mdadm: no RAID superblock on /dev/sde.
>
> As has been mentioned elsewhere, mdadm only recognised IMSM arrays on
> machines with IMSM hardware.  I'm not entirely happy about this and may well
> change it.
>
>
>>
>> # mdadm --examine /dev/sde
>> /dev/sde:
>>           Magic : Intel Raid ISM Cfg Sig.
>>         Version : 1.1.00
>>     Orig Family : 5a8ed623
>>          Family : 5a8ed623
>>      Generation : 00000000
>>            UUID : ae2e9cd8:7fa43248:47c694a1:24990cbc
>>        Checksum : c23b6c88 correct
>>     MPB Sectors : 1
>>           Disks : 2
>>    RAID Devices : 1
>>
>>   Disk00 Serial : 66faec8-9f5b237d
>>           State : active
>>              Id : 00040000
>>     Usable Size : 1019486 (497.88 MiB 521.98 MB)
>>
>> [testF]:
>>            UUID : 6640a4cc:5faa1ce3:c1bff2b3:1093ca7d
>>      RAID Level : 1
>>         Members : 2
>>           Slots : [UU]
>>     Failed disk : none
>>       This Slot : 0
>>      Array Size : 1014446 (495.42 MiB 519.40 MB)
>>    Per Dev Size : 1014792 (495.59 MiB 519.57 MB)
>>   Sector Offset : 0
>>     Num Stripes : 3963
>>      Chunk Size : 64 KiB
>>        Reserved : 0
>>   Migrate State : idle
>>       Map State : normal
>>     Dirty State : clean
>>
>>   Disk01 Serial : 0b540c6-4e527908
>>           State : active
>>              Id : 00050000
>>     Usable Size : 1019486 (497.88 MiB 521.98 MB)
>>
>>
>> Do not you think that dmraid should also ship an udev rules file to
>> mount the raid which can handle?
>
> I have no opinion about what dmraid should do.  I have enough trouble working
> out what mdadm should do :-)
>
Thanks Neil, it's more clear.

Regards,

-- 
Sébastien Luttringer
www.seblu.net
--
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

Re: Mdadm, udev and fakeraid?

[Dan Williams]

On Sun, Apr 17, 2011 at 5:38 PM, NeilBrown <neilb@suse.de> wrote:
> On Fri, 15 Apr 2011 16:15:50 +0200 Seblu <seblu@seblu.net> wrote:
>
>> On Tue, Apr 5, 2011 at 8:20 AM, NeilBrown <neilb@suse.de> wrote:
>> > On Sun, 3 Apr 2011 18:03:50 +0200 Seblu <seblu@seblu.net> wrote:
>> >
>> >> Hello,
>> >>
>> >> In the following commit, udev rules load isw_raid (fakeraid). From my
>> >> test, this doesnt work. I have to call dmraid to have something
>> >> working.
>> >> http://neil.brown.name/git?p=mdadm;a=commit;h=475a01b8bce8575dd1b2ab6495e65e854702ac0e
>> >>
>> >> isw_raid is only fakeraid devices? mdadm is able to mount fakeraid partition?
>> >>
>> >
>> > I'm sorry but I cannot parse those questions successfully so I'm not sure
>> > what you are asking.
>>
>> Hello Neil,
>>
>> in my previous mail, i used word fakeraid about raid created with
>> dmraid and i used softraid about raid created with mdadm. it was not
>> clear.
>>
>> So my question was about compatibily. Raids created by dmraid can be
>> assembled with mdadm and vice versa?
>>
>> > Both dmraid and mdadm can manage some 'fakeraid' arrays.  dmraid supports a
>> > wider variety.  mdadm supports raid1 and raid5 more completely than dmraid
>> > does.
>> mdadm -> create soft raid for linux  (now there is new format: ddf and imsm) ?
>> dmraid -> create soft raid from industry raid card format  ?
>
> No, it isn't that simple.
>
> dmraid uses the 'dm' kernel module.  mdadm uses the 'md' kernel module.
>
> As such dmraid doesn't support RAID5 (yet) and doesn't support RAID1 very
> well.
> mdadm supports both of these well, but doesn't support the same range of
> "industry raid card formats".
>
> There is a growing amount of overlap.
>
>>
>> > Both should support isw to some degree.
>> > Intel are currently working with mdadm to make it provide full support for
>> > "IMSM" (Intel Matrix Storage Manager).  I don't know the exact relationship
>> > between 'isw' and 'IMSM' - maybe they are different names for the same thing.
>> ok
>>
>> > If mdadm doesn't work for your isw arrays, and you want it to, then I suggest
>> > you report details about what is, or is not, happening.
>> My purpose is to improve archlinux startup detection of fakeraids
>> (mdadm + dmraid).
>>
>> With mdadm everything works correctly without call to "mdadm -As"
>> With dmraid, no raid is created by udev rules, so we need to run
>> "dmraid -i -ay" at startup.
>>
>> To test this kind of raid, i created a dmraid array in a vm. This
>> created me a /dev/mapper/isw_bfbjdbadhb_testF device.
>> call blkid on a disk member of this raid tell me this:
>> /dev/sde: TYPE="isw_raid_member"
>> and on "mdadm" created raid:
>> /dev/sdd: UUID="a974b525-993a-1481-f860-6471f3f120e1"
>> UUID_SUB="eb22aee2-b2ee-e56d-1008-44d52c63564d" LABEL="archipel:0"
>> TYPE="linux_raid_member"
>>
>> This misled me because mdadm udev rules uses the output of blkid to
>> mount raids which have type "isw_raid_member".
>> What disturbs me is that mdadm cannot mount raid created by dmraid
>> with type isw_raid_member.
>>
>> About outputs:
>> mdadm -I --verbose /dev/sde
>> mdadm: no RAID superblock on /dev/sde.

Seblu can you verify that:
    export IMSM_NO_PLATFORM=1
    mdadm -E /dev/sde

finds no superblock? It may be that dmraid has laid down something incompatible.

> As has been mentioned elsewhere, mdadm only recognised IMSM arrays on
> machines with IMSM hardware.  I'm not entirely happy about this and may well
> change it.

I have trouble answering the "least surprise" question in this area.

Is it more surprising to go into your BIOS, explicitly turn off raid
support and still see raid devices showing up?

Or is it more surprising to take a raid array from a raid enabled
system to raid disabled system and wonder why things won't assemble?

For safety I think it is better if mdadm not perform operations that
might be incompatible with the platform option-rom.  But if you need
to recover to a usb attached drive, or some other
platform-incompatible configuration, you can use the environment
variable in a pinch.

--
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

Re: Mdadm, udev and fakeraid?

[NeilBrown]

On Fri, 22 Apr 2011 19:37:40 -0700 Dan Williams <dan.j.williams@gmail.com>
wrote:

> On Sun, Apr 17, 2011 at 5:38 PM, NeilBrown <neilb@suse.de> wrote:

> > As has been mentioned elsewhere, mdadm only recognised IMSM arrays on
> > machines with IMSM hardware.  I'm not entirely happy about this and may well
> > change it.
> 
> I have trouble answering the "least surprise" question in this area.
> 
> Is it more surprising to go into your BIOS, explicitly turn off raid
> support and still see raid devices showing up?

Is the "RAID support has been explicitly turned off" state visible from a
running kernel? or is it indistinguishable from "platform does not have RAID
support"?

> 
> Or is it more surprising to take a raid array from a raid enabled
> system to raid disabled system and wonder why things won't assemble?
> 
> For safety I think it is better if mdadm not perform operations that
> might be incompatible with the platform option-rom.  But if you need
> to recover to a usb attached drive, or some other
> platform-incompatible configuration, you can use the environment
> variable in a pinch.

There are 3 interesting cases:  create, assemble, examine.
(grow might be interesting too, but for now it would be confusing).

I am perfectly happy for 'create' to be arbitrarily hard if platform support
is not available.  One is unlikely to want to create an array in that case
anyway.
I think 'examine' should always show whatever it can, which is the case for
3.2.1.  Possibly it should also give a warning about  any difficulty that
might be experienced in assembling the array.

Assemble in the interesting case.  The law of least surprise requires it to
either work or give a good error message.  Your suggestion that it possibly
should not work in some cases seems defensible, so at least a very clear
error message would be good.
As for how to over-ride the default caution - I would prefer --force to
achieve it rather than requiring an environment variable.  I would possibly
accept --force-platform (or similar) but I think --force should be sufficient.

What think you?

Thanks,
NeilBrown
--
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

Re: Mdadm, udev and fakeraid?

[Seblu]

On Sat, Apr 23, 2011 at 4:37 AM, Dan Williams <dan.j.williams@gmail.com> wrote:
> On Sun, Apr 17, 2011 at 5:38 PM, NeilBrown <neilb@suse.de> wrote:
>> On Fri, 15 Apr 2011 16:15:50 +0200 Seblu <seblu@seblu.net> wrote:
>>
>>> On Tue, Apr 5, 2011 at 8:20 AM, NeilBrown <neilb@suse.de> wrote:
>>> > On Sun, 3 Apr 2011 18:03:50 +0200 Seblu <seblu@seblu.net> wrote:
>>> >
>>> >> Hello,
>>> >>
>>> >> In the following commit, udev rules load isw_raid (fakeraid). From my
>>> >> test, this doesnt work. I have to call dmraid to have something
>>> >> working.
>>> >> http://neil.brown.name/git?p=mdadm;a=commit;h=475a01b8bce8575dd1b2ab6495e65e854702ac0e
>>> >>
>>> >> isw_raid is only fakeraid devices? mdadm is able to mount fakeraid partition?
>>> >>
>>> >
>>> > I'm sorry but I cannot parse those questions successfully so I'm not sure
>>> > what you are asking.
>>>
>>> Hello Neil,
>>>
>>> in my previous mail, i used word fakeraid about raid created with
>>> dmraid and i used softraid about raid created with mdadm. it was not
>>> clear.
>>>
>>> So my question was about compatibily. Raids created by dmraid can be
>>> assembled with mdadm and vice versa?
>>>
>>> > Both dmraid and mdadm can manage some 'fakeraid' arrays.  dmraid supports a
>>> > wider variety.  mdadm supports raid1 and raid5 more completely than dmraid
>>> > does.
>>> mdadm -> create soft raid for linux  (now there is new format: ddf and imsm) ?
>>> dmraid -> create soft raid from industry raid card format  ?
>>
>> No, it isn't that simple.
>>
>> dmraid uses the 'dm' kernel module.  mdadm uses the 'md' kernel module.
>>
>> As such dmraid doesn't support RAID5 (yet) and doesn't support RAID1 very
>> well.
>> mdadm supports both of these well, but doesn't support the same range of
>> "industry raid card formats".
>>
>> There is a growing amount of overlap.
>>
>>>
>>> > Both should support isw to some degree.
>>> > Intel are currently working with mdadm to make it provide full support for
>>> > "IMSM" (Intel Matrix Storage Manager).  I don't know the exact relationship
>>> > between 'isw' and 'IMSM' - maybe they are different names for the same thing.
>>> ok
>>>
>>> > If mdadm doesn't work for your isw arrays, and you want it to, then I suggest
>>> > you report details about what is, or is not, happening.
>>> My purpose is to improve archlinux startup detection of fakeraids
>>> (mdadm + dmraid).
>>>
>>> With mdadm everything works correctly without call to "mdadm -As"
>>> With dmraid, no raid is created by udev rules, so we need to run
>>> "dmraid -i -ay" at startup.
>>>
>>> To test this kind of raid, i created a dmraid array in a vm. This
>>> created me a /dev/mapper/isw_bfbjdbadhb_testF device.
>>> call blkid on a disk member of this raid tell me this:
>>> /dev/sde: TYPE="isw_raid_member"
>>> and on "mdadm" created raid:
>>> /dev/sdd: UUID="a974b525-993a-1481-f860-6471f3f120e1"
>>> UUID_SUB="eb22aee2-b2ee-e56d-1008-44d52c63564d" LABEL="archipel:0"
>>> TYPE="linux_raid_member"
>>>
>>> This misled me because mdadm udev rules uses the output of blkid to
>>> mount raids which have type "isw_raid_member".
>>> What disturbs me is that mdadm cannot mount raid created by dmraid
>>> with type isw_raid_member.
>>>
>>> About outputs:
>>> mdadm -I --verbose /dev/sde
>>> mdadm: no RAID superblock on /dev/sde.
>
> Seblu can you verify that:
>    export IMSM_NO_PLATFORM=1
>    mdadm -E /dev/sde

archipel ~ 0 # export IMSM_NO_PLATFORM=1
archipel ~ 1 # mdadm -E /dev/sde
/dev/sde:
          Magic : Intel Raid ISM Cfg Sig.
        Version : 1.1.00
    Orig Family : 5a8ed623
         Family : 5a8ed623
     Generation : 00000000
           UUID : ae2e9cd8:7fa43248:47c694a1:24990cbc
       Checksum : c23b6c88 correct
    MPB Sectors : 1
          Disks : 2
   RAID Devices : 1

  Disk00 Serial : 66faec8-9f5b237d
          State : active
             Id : 00040000
    Usable Size : 1019486 (497.88 MiB 521.98 MB)

[testF]:
           UUID : 6640a4cc:5faa1ce3:c1bff2b3:1093ca7d
     RAID Level : 1
        Members : 2
          Slots : [UU]
    Failed disk : none
      This Slot : 0
     Array Size : 1014446 (495.42 MiB 519.40 MB)
   Per Dev Size : 1014792 (495.59 MiB 519.57 MB)
  Sector Offset : 0
    Num Stripes : 3963
     Chunk Size : 64 KiB
       Reserved : 0
  Migrate State : idle
      Map State : normal
    Dirty State : clean

  Disk01 Serial : 0b540c6-4e527908
          State : active
             Id : 00050000
    Usable Size : 1019486 (497.88 MiB 521.98 MB)

>
> finds no superblock? It may be that dmraid has laid down something incompatible.
>
>> As has been mentioned elsewhere, mdadm only recognised IMSM arrays on
>> machines with IMSM hardware.  I'm not entirely happy about this and may well
>> change it.
>
> I have trouble answering the "least surprise" question in this area.
>
> Is it more surprising to go into your BIOS, explicitly turn off raid
> support and still see raid devices showing up?
>
> Or is it more surprising to take a raid array from a raid enabled
> system to raid disabled system and wonder why things won't assemble?
>
> For safety I think it is better if mdadm not perform operations that
> might be incompatible with the platform option-rom.  But if you need
> to recover to a usb attached drive, or some other
> platform-incompatible configuration, you can use the environment
> variable in a pinch.
>
> --
> Dan
>



-- 
Sébastien Luttringer
www.seblu.net
--
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

Re: Mdadm, udev and fakeraid?

[Luca Berra]

On Sat, Apr 23, 2011 at 06:45:51PM +1000, NeilBrown wrote:
>On Fri, 22 Apr 2011 19:37:40 -0700 Dan Williams <dan.j.williams@gmail.com>
>wrote:
>
>> On Sun, Apr 17, 2011 at 5:38 PM, NeilBrown <neilb@suse.de> wrote:
>
>> > As has been mentioned elsewhere, mdadm only recognised IMSM arrays on
>> > machines with IMSM hardware.  I'm not entirely happy about this and may well
>> > change it.
>> 
>> I have trouble answering the "least surprise" question in this area.
>> 
>> Is it more surprising to go into your BIOS, explicitly turn off raid
>> support and still see raid devices showing up?
>
>Is the "RAID support has been explicitly turned off" state visible from a
>running kernel? or is it indistinguishable from "platform does not have RAID
>support"?
you can try guessing, intel controllers change their pci product_id based on the
mode they are set to operate in bios.

L.

-- 
Luca Berra -- bluca@comedia.it
--
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