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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.


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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