Re: Linux mdadm superblock question.

[Michael Evans <mjevans1983@gmail.com>]

On Sat, Feb 13, 2010 at 12:37 AM, Giovanni Tessore <giotex@texsoft.it> wrote:
>
>> I may be converting a host to ext4 and was curious, is 0.90 still the only
>> superblock version for mdadm/raid-1 that you can boot from without having to
>> create an initrd/etc?
>>
>> Are there any benefits to using a superblock > 0.90 for a raid-1 boot
>> volume < 2TB?
>
> I recently reinstalled my systems, and I had to use superblock 0.9 to be
> able to boot ext4 from raid-1 (kernel 2.6.31 - grub2 1.97-beta4).
> I didn't go deep with it as I was quite in hurry, so I'm not sure if it
> depends by grub2 or by kernel's md autodetection at boot.
> I used superblock 1.1 for the others md devices.
>
> The advantage of superblocks >= 1.0 that I prefere is that they persist the
> number of recovered read errors; this allow to monitor (at the moment
> manually via /sys/block/mdXX/devYY/errors) across system restarts the health
> of devices into the array, useful for raid-5 and 2-disks raid-1.
>
> Regards
>
> --
> Cordiali saluti.
> Yours faithfully.
>
> Giovanni Tessore
>
>
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mdadm 1.0 block devices, since stored at the end, can still be used
/read only/ the same way that 0.90 devices were used before grub knew
how to talk to them.  By looking at the underlying block devices and
ignoring their tails.  This does however only hold for raid-1 layouts
with the 1.0 or 0.90 format labels.
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