Bug#462617: debian-installer: need RAID bitmap support (mdadm -b internal)
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.
-- System Information:
Debian Release: 4.0
APT prefers stable
APT policy: (500, 'stable')
Architecture: i386 (i686)
Shell: /bin/sh linked to /bin/bash
Kernel: Linux 2.6.18-5-686
Locale: LANG=en_AU.UTF-8, LC_CTYPE=en_AU.UTF-8 (charmap=ANSI_X3.4-1968) (ignored: LC_ALL set to C)
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