From: Neil Brown <neilb@suse.de>
To: Bill Davidsen <davidsen@tmr.com>
Cc: Jan Engelhardt <jengelh@computergmbh.de>, linux-raid@vger.kernel.org
Subject: Re: Some RAID levels do not support bitmap
Date: Tue, 12 Jun 2007 09:39:14 +1000 [thread overview]
Message-ID: <18029.56610.868907.654059@notabene.brown> (raw)
In-Reply-To: message from Bill Davidsen on Monday June 11
On Monday June 11, davidsen@tmr.com 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?
NeilBrown
next prev parent reply other threads:[~2007-06-11 23:39 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-06-11 12:50 Some RAID levels do not support bitmap Jan Engelhardt
2007-06-11 23:15 ` Bill Davidsen
2007-06-11 23:39 ` Neil Brown [this message]
2007-06-12 15:52 ` Bill Davidsen
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