Date: Wed, 11 Aug 1999 08:48:38 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Michael Vernick <vernick@bell-labs.com> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: Help with understand file system performance Message-ID: <32009.934354118@critter.freebsd.dk> In-Reply-To: Your message of "Tue, 10 Aug 1999 15:32:13 EDT." <37B07E3D.16F2B334@bell-labs.com>
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In message <37B07E3D.16F2B334@bell-labs.com>, Michael Vernick writes: >My results show that: > >1. Performance degrades significantly (15-20%) when going from 1 to 2 >processes then slowly increases as more processes are run. The same >performance is achieved when running a single reader vs. running 8 >readers. This happens for each type of directory structure. That is a good sign: It means that you don't have to do unnatural things to your application to get full throughput out of our file system. >2. Performance degrades about 15% for the 1 process experiment when the >files are split across 2 file systems vs. a single file system. This >one has me somewhat perplexed. Is it because there is more directory >information thrashing from disk to memory? That sounds weird... Do you have twice as many directories this way ? Or are the two filesystems on the same physical disk ? if so you are seeking much more. >3. On a per process basis, performance increases when the number of >files per directory increases/number of subdirs decreases. Is this >because there is a better chance the directory information about the >file could be in memory? Yes. The minimum directory size is the fragsize of the filesystem, filling the directories better means better performance. >Our goal, of course, it to maximize performance. So any help in the >tuning of our system (i.e. reading lots of ~15KB files) would be >appreciated Try fiddling the newfs parameters. I see 17% speedup using: newfs -b 16384 -f 4096 -c 100 Try to fill your directories so they are just below the fragment size of the filesystem (Ie: <1024 bytes for no newfs options, < 4096 bytes with the above options). -- Poul-Henning Kamp FreeBSD coreteam member phk@FreeBSD.ORG "Real hackers run -current on their laptop." FreeBSD -- It will take a long time before progress goes too far! To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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