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Re: [Gluster-devel] performance improvements


From: Vincent Régnard
Subject: Re: [Gluster-devel] performance improvements
Date: Wed, 24 Oct 2007 16:12:58 +0200
User-agent: Thunderbird 2.0.0.6 (X11/20070728)

Daniel van Ham Colchete a écrit :
On 10/23/07, Vincent Régnard <address@hidden> wrote:
Hi all,

The afr synchronisation using "find -mtime -1 -type f -exec head -c1
trick" takes approximately 30 minutes for a 20GB filesystem with 300.000
files. Which seems too long to be acceptable for us. I'd like to tune
some parameters to increase performance.

Vincent.

Vicent,

so, in 1800 seconds you lookup(), open(), read() and close() 300.000 times?
That's 6ms for each file, and that's really good. Are you sure you
interconnect has a 5ms round-trip time? I would bet it is less.

Hi Daniel, and thank you for your clear answer.

Actually, according to logs I have, only about a hundred file is modified every day, so open() read() and close() only occur for these 100 files. Not the whole filesystem. So half an hours seams a long time for that ? I now do this file synchronisation on a per directory basis (only directories where I know changes might occur) to reduce the runtime and it actually runs much faster. find command really seams to spend a huge time going down and up in the whole directory tree. I tried to do the same operation for all the files (not restrincting to recently modified), so this means opening etc.. all the 300.000 files, but untill now I never managed to get it finish (beeing trying for 2 weeks now) ! Either glusterfs crashes before or I have to stop client or server for another reason (software upgrade). I had it run once for more than 12 hours, but it did not complete.


IMO, usually you shouldn't measure GlusterFS performance with things
happening serially. GlusterFS is really good when things are happening in
parallel. I prefer to measure a network filesystem performance not on how
much time it takes to do one operation, but on how many operations it can do
in at the same time. If you had 300 threads trying to read all those files
it would be a lot faster. Usually that's the way real utilization happens,
if you have a webserver and a mail server using your storage, you will have
lots of web requests and e-mail sessions reading and writing at the same
time.


Regarding read/write access, I monitor with 10 clients in parralel (I can see the activity of 10 gluster threads). This seams ok to me, I have between 5 and 2 MB/s on a 100Mb network. But there is certainly no readdir() in that case, at least not in directories with many files. My real problem is listing files in directory. Mainly for mail purpose (smtp+imap server). I have not performed any test yest, but transfering to glusterfs my maildirs with about 10.000 files each really frightens me.

I also made some tests restricting the configuration to client and servers in the same datacenter (round-trip about .1ms), but the result seems to be roughly the same regarding read/write performance.

--
Vincent Régnard
address@hidden
TBS-internet.com
027 630 5902




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