Re: metadata versions: 0.90 vs 1.2

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On 13/06/2012 06:55, plug bert wrote:
Hello,

i noticed this while twiddling with RAID1 arrays...

On our old CentOS 4.7 box, i can mount a RAID1 array member
independently of the array -- i.e. mount /dev/sdc1 /mountpoint....but
on CentOS 5.x and later i am met with an unknown filesystem:
linux_raid_member error.

Somebody hinted that this had something to do with the metadata
versions, so i recreated the RAID1 array on CentOS 5.x with the
--metadata=0.90 parameter...and was able to mount the array member
w/o any problems.


Is this expected behavior? Are there any potential problems if i
stick with metadata=0.90(apart from the 28 device and 2Tb disk space
limit)?


Yes, this is expected behaviour (as Mikael explained).

As for potential problems, the big one is if you mount a member of a raid1 array (with metadata 0.90, 1.0) directly, and write to it, you'll corrupt the raid1 array. So make sure you only mount it read-only, unless you never want to see the raid1 again.

Typical uses of such mounts are for recovery purposes, or for accessing the raid from a bootloader (newer grub can understand more raid arrays, but raid1 with metadata 0.90 is often used with older grub).


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