From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Some RAID levels do not support bitmap Date: Tue, 12 Jun 2007 11:52:47 -0400 Message-ID: <466EC14F.1080501@tmr.com> References: <466DD7AF.7030107@tmr.com> <18029.56610.868907.654059@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <18029.56610.868907.654059@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Jan Engelhardt , linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > 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? 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 CTO TMR Associates, Inc Doing interesting things with small computers since 1979