URGENT: Need help rebuilding iir RAID5 array with failed drive

Derek Ragona derek at computinginnovations.com
Fri Jun 27 22:06:54 UTC 2008

At 10:04 PM 6/26/2008, 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?!?!

Most if these RAID's are done in the BIOS so the OS sees just a 
volume.  The RAID 5 or RAID 1, or RAID 0, or various combinations are left 
to the BIOS.

Also these are considered software RAIDS not hardware as the BIOS uses the 
Motherboard CPU.


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