Re: Mdadm, udev and fakeraid?

[Seblu <seblu@seblu.net>]

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
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