From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Some RAID levels do not support bitmap Date: Mon, 11 Jun 2007 19:15:59 -0400 Message-ID: <466DD7AF.7030107@tmr.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Jan Engelhardt Cc: linux-raid@vger.kernel.org, neilb@suse.de List-Id: linux-raid.ids 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 CTO TMR Associates, Inc Doing interesting things with small computers since 1979