Re: Some RAID levels do not support bitmap

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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.

BTW: RAID-4 seems to work fine with an external bitmap. Were you trying to do "internal?"

--
bill davidsen <davidsen@xxxxxxx>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979

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