From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miles Fidelman Subject: Re: RAID6 and crashes (reporting back re. --bitmap) Date: Fri, 11 Jun 2010 16:26:01 -0400 Message-ID: <4C129BD9.1020304@meetinghouse.net> References: <4C1128C2.4020105@meetinghouse.net> <20100611005743.43664e5b@natsu> <4C11578B.8010202@meetinghouse.net> <20100611034108.6a2cdbc4@natsu> <4C1169CB.1030903@meetinghouse.net> <20100611085112.5f33b06f@natsu> <4C11BFB7.7050907@meetinghouse.net> <20100611105521.67c9658c@natsu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100611105521.67c9658c@natsu> Sender: linux-raid-owner@vger.kernel.org Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids FYI: I just: - removed the bitmap - installed a new bitmap with larger chunk-size on 4 arrays, on each of two machines (redundant high-availability cluster setup) Took me all of about 5 minutes, of which most of the time was waiting for virtual machines to migrate from one machine to the other, and then back. All seems to be working, performance seems just a little snappier - but who can really tell until the next time an array rebuilds. Thanks all (and Roman in particular) for your guidance. Miles Roman Mamedov wrote: > On Fri, 11 Jun 2010 00:46:47 -0400 > Miles Fidelman wrote: > > >> Looks like my original --bitmap internal creation set a very large chunk >> size initially >> >> md3 : active raid6 sda4[0] sdd4[3] sdc4[2] sdb4[1] >> 947417088 blocks level 6, 64k chunk, algorithm 2 [4/4] [UUUU] >> bitmap: 6/226 pages [24KB], 1024KB chunk >> >> unless that --bitmap-chunk=131072 recommendation is translates to >> 131072KB (if so, are you really running 131MB chunks?) >> > Yes, this is correct. > This will only mean that after an unclean shutdown, at least 128MB-sized > areas of the array will be invalidated for a resync, and not smaller areas > with 1MB-granularity like on yours currently. 128 megabytes is just about 1 > second of read throughput on modern drives, so I am okay with that. Several > 128MB-windows here and there are still faster to resync than the whole array. > And this had an extemely good effect on write performance for me (increased it > by more than 1.5x) compared to a small chunk. Test for yourself, first without > the bitmap, then with various chunk sizes of it (ensure there's no other load > on the array, and note the speeds): > > dd if=/dev/zero of=/your-raid/zerofile bs=1M count=2048 conv=notrunc,fdatasync > > -- In theory, there is no difference between theory and practice. In practice, there is. .... Yogi Berra