Bill Told me to report this to linux-raid. But Possibly the raid code can't be blamed, because it is the filesystem code that messes up. ----- Forwarded message from Bill Davidsen <davidsen@xxxxxxx> ----- > > From: Bill Davidsen <davidsen@xxxxxxx> > To: Rogier Wolff <R.E.Wolff@xxxxxxxxxxxx> > CC: linux-kernel@xxxxxxxxxxxxxxx > Date: Thu, 05 Jul 2007 15:35:36 -0400 > Subject: Re: RAID performance is not too well.... > X-Spam-Status: No, score=3.0 required=5.0 tests=AWL,BAYES_99 autolearn=no version=3.1.7-deb > Rogier Wolff wrote: > >Hi, > > > >I have an application that creates some 228 thousand files, > >spread over about 4000 directories. Total is not more than > >1.3Gb. (I'm not sure, and I don't care if it's 10% or 90% of > >that number) > > > >Anyway, I've loaded all of the 1.3Gb into the cache (the machine > >has 8Gb of RAM), so that only writes need to take place. > > > >After a while the machine goes into a routine of writing > >about 500 to 1000kbytes per second. > > > >Sync seems to take a long time: > > > >zebigbos:/recover7/bd4256_jense/tree> time sync > >0.004u 0.136s 5:44.66 0.0% 0+0k 0+0io 0pf+0w > >zebigbos:/recover7/bd4256_jense/tree> > > > >The machine normally reads up to about 150 Mbytes per second without > >trouble. > > > >I'm suspecting that the writes to the inodes and files all end > >up "fragmented" such that reads to complete the RAID stripes > >need to be performed: > > > >Iostat shows: > > > >Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn > >sda 75.25 277.23 126.73 280 128 > >sdb 91.09 400.00 134.65 404 136 > >sdc 71.29 253.47 95.05 256 96 > >sdd 100.99 221.78 304.95 224 308 > > > >However, I would say that all those new files should be "clustered" > >such that the chances of writing a full stripe becomes reasonable. > >Moreover, clustering should, even with reading other parts of the > >stripe result in a performance on the order of 10 to 50 times better. > > > >Raid block (stripe) size is 64k. (Next time I format a partition, This should be chunk size. ^^^^^^^^ > >I will chose 512k, causing the readperformance to increasae from 150Mb > >per second to about 200Mb per second). > > > I'm not sure what you mean by "Raid block," and a stripe size on 64k is > improbably low. That sounds like a chunk size using common nomenclature. OK. chunk size. > You don't say what RAID level you are using, nor what filesystem type, RAID 5. > so it's really hard to give you any useful help, other than "send more > information, use standard terms, send to the linux-raid list, not kernel." > > By "format a partition" do you mean "create an array?" Or ??? Ehh. Yes. Roger. -- ** R.E.Wolff@xxxxxxxxxxxx ** http://www.BitWizard.nl/ ** +31-15-2600998 ** ** Delftechpark 26 2628 XH Delft, The Netherlands. KVK: 27239233 ** *-- BitWizard writes Linux device drivers for any device you may have! --* Q: It doesn't work. A: Look buddy, doesn't work is an ambiguous statement. Does it sit on the couch all day? Is it unemployed? Please be specific! Define 'it' and what it isn't doing. --------- Adapted from lxrbot FAQ - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
