[RndTbl] Big-endian RAID5 recovery problem

NeilBrown neilb at suse.com
Sat May 6 00:57:17 CDT 2017

On Mon, May 01 2017, Adam Thompson wrote:

> So I've got 4 IDE HDDs, each with 3 RAID partitions on them, that were 
> part of a RAID array in a now-very-dead NAS.
> Of course, I need to get data off them that wasn't backed up anywhere 
> else.
> I've got a 4-port USB3 PCIe card, and 4 IDE/SATA USB adapters, and all 
> the hardware seems to work.  So far, so good.
> The problem is that the disks use the v0.90 metadata format, and they 
> came from a big-endian system, not a little-endian system.  MD 
> superblocks *since* v0.90 are endian-agnostic, but back in v0.90, the 
> superblock was byte-order specific.
> mdadm(8) on an Intel processor refuses to acknowledge the existence of 
> the superblock.  Testdisk detects it and correctly identifies it as a 
> Big-endian v0.90 superblock.
> I'm reluctant to blindly do a forced --create on the four disks, because 
> I'm not 100% certain of the RAID topology; there are at least two RAID 
> devices, one of which was hidden from the user, so I have no a-priori 
> knowledge of its RAID level or layout.
> The filesystems on the md(4) devices are, AFAIK, all XFS, and so should 
> (hopefully) not have any endianness issues.
> I can't find any modern big-endian Linux systems... looks like all the 
> ARM distros run in little-endian mode.
> Any suggestions on the best way to move forward?

Look for "--update=byteorder" in the mdadm man page.

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