URGENT: Need help rebuilding iir RAID5 array with failed drive

[Benjamin Close]

Garrett Cooper wrote:
> On Thu, Jun 26, 2008 at 8:44 AM, Benjamin Close
> <Benjamin.Close at clearchain.com> wrote:
>   
>> Tom Evans wrote:
>>     
>>> On Thu, 2008-06-26 at 06:49 -0700, Garrett Cooper wrote:
>>>
>>>       
>>>> Hello,
>>>>      First off sorry for the cross-post. I typically don't do this
>>>> but this is an important question, so please bear with me. I'm just
>>>> trying to get more eyes on the subject so I can (maybe) get a reply
>>>> quicker...
>>>>      I'm running 8-CURRENT on my machine and it appears that one of
>>>> the disks in my RAID5 array has taken a nose dive (BIOS recognizes
>>>> that it exists, but Intel Matrix Manager claims that the disk is an
>>>> "Offline Member"). After doing some reading it appears that it's
>>>> kaput, so I need to get a replacement disk to fix this one...
>>>>      That aside, I need to determine how to rebuild the array in a
>>>> Unix environment because Intel only provides instructions for how to
>>>> use their Windows matrix manager. If anyone can point me to some links
>>>> or provide me with some pointers on how to correct this issue, I'd owe
>>>> you a lot; in fact the next time you come by Santa Cruz, CA I'll
>>>> gladly treat you to some beers or something else you might want :)...
>>>> Linux solutions (if there isn't a proper one for FreeBSD) are valid,
>>>> as long as the core data remains uncorrupted and I can do what I need
>>>> to from a LiveCD. I'm just scared to boot up OS and have it do some
>>>> irrevocable operation like fsck -y and assume parity errors are ok or
>>>> something along those lines  (I don't remember if I set rc.conf to
>>>> fsck -y and I know I can change that from single-user mode, but I want
>>>> to play things conservatively if at all possible) :\...
>>>>      Filesystem is UFS2 with softupdates of course.
>>>>      Point proven that I need to backup my data more often :(...
>>>> TIA,
>>>> -Garrett
>>>>
>>>> PS If replying on the questions@ list, please CC me as I'm not
>>>> subscribed to that list.
>>>>
>>>>         
>>> I'm fairly sure that Intel Matrix metadata cant be created/modified by
>>> fbsd, only read. You should be able to do whatever rebuild operations
>>> you need in the BIOS I believe, but that would be an offline operation,
>>> clearly.
>>>
>>> I may be mistaken, and the driver can handle array rebuilds for matrix.
>>> If it can, the command you are looking for is 'atacontrol rebuild ar0',
>>> see atacontrol(8).
>>>
>>> Tom
>>>
>>>       
>> Please DONT use FreeBSD to rebuild this RAID5 unit. FreeBSD will detect it
>> as a raid 5 Unit and even allow you to use it, add the new disk to it and
>> even let you rebuild the raid.
>> However the ata driver does not have support parity for Raid5. From
>> ataraid(4):
>>
>>    RAID5 is not supported at this time.  Code exists, but it neither uses
>>    nor maintains parity information.
>>
>> You can confirm this in code, just look for the Swedish comments in
>> ataraid.c
>> Hence writing to the raidset will give you a glorified raid0.
>>
>> Cheers,
>>   Benjamin
>>     
>
> So.. wait a sec? Are you saying I'm fscked because my RAID5 is nothing
> more than RAID0 under FreeBSD?!?!
>   
If you've been writing to the RAID5 under FreeBSD, then yes. You've got 
a glorified paper weight and sadly your data is most likely lost.
I've had a bug report 
http://www.freebsd.org/cgi/query-pr.cgi?pr=bin/106431 unanswered for 
some time about at least warning users about this.
For the future I'd recommend either zfs of the geom suite (gmirror, etc).

Benjamin