Bug#462617: debian-installer: need RAID bitmap support (mdadm -b internal)
reassign 462617 mdcfg
thanks
Russell Coker <russell@coker.com.au> writes:
> Package: debian-installer
> Severity: normal
>
> A recent (some time in the last 5 years) feature of Linux software RAID is a
> "write intent bitmap". The purpose of this is that before writing to a
> section of disk the bitmap is altered to mark it as dirty. Then if the
> machine experiences a power failure or other catastrophic event then when
> rebooted it will know that the section referenced by that bit is dirty.
>
> Thus on reboot after a serious failure small amounts of data will be
> synchronised instead of large amounts.
>
> This feature is not currently used by the Debian installer. So if you
> install to a system with multiple disks in a RAID-1 array (and probably
> RAID-5 and RAID-6) then every time there is a power failure the disks in
> the RAID will have to be completely read to ensure that they match.
>
> If the mdadm command that was used for the Debian installer had "-b internal"
> appended then the bitmap feature would be used and recovery from some failure
> conditions would be much faster. There does not seem to be any down-side to
> using this.
>
> I have not tested this with RAID-5 and RAID-6, but have tested the benefits
> of this option for RAID-1 and found it to be very useful.
I've reassign this bug to mdcfg that's where it needs to be
change and added Martin (madduck) as Cc since he's the maintainer of
mdadm on Debian.
Please Martin, could you comment on that?
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