Neil Brown wrote:
On Monday June 11, davidsen@xxxxxxx wrote:
Jan Engelhardt wrote:
Hi,
RAID levels 0 and 4 do not seem to like the -b internal. Is this
intentional? Runs 2.6.20.2 on i586.
(BTW, do you already have a PAGE_SIZE=8K fix?)
14:47 ichi:/dev # mdadm -C /dev/md0 -l 4 -e 1.0 -b internal -n 2 /dev/ram[01]
mdadm: RUN_ARRAY failed: Input/output error
mdadm: stopped /dev/md0
14:47 ichi:/dev # mdadm -C /dev/md0 -l 0 -e 1.0 -b internal -n 2 /dev/ram[01]
mdadm: RUN_ARRAY failed: Cannot allocate memory
mdadm: stopped /dev/md0
Right... md: bitmaps not supported for this level.
Bitmaps show what data has been modified but not written. For RAID-0
there is no copy, therefore there can be no bitmap to show what "still
needs to be updated." I would have thought that RAID-4 would support
bitmaps, but maybe it was just never added because use of RAID-4 is
pretty uncommon.
"added late" rather than "never added". 2.6.21 supports bitmaps on
RAID-4, The patch is about 2 lines and would apply to 2.6.20 with no
trouble.
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=3d37890baa4ca962f8a6b77525b8f3d0698eee09
BTW: RAID-4 seems to work fine with an external bitmap. Were you trying
to do "internal?"
I suspect you were using 2.6.21-rc6 or later?
No, the machine I had for trial was 2.6.15 with a few patches, none in
RAID. Seemed to work just fine if I put the bitmap on an external
device. Was that not as expected?
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979
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