debian-installer and software RAID
A recent 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.
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=462617
I've filed a bug report about this at the above URL, but I'd like some input
from the people on this list.
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