On 26.04.2010 14:37, mailinglists@belfin.ch wrote:
Hi,
I would like to run my imap service on a active-active cluster. I wonder how well OCFS2 performs in read and write with millions of smallest files involved. Has anybody got any experience?
Thanks John
I have some experience.
I have done some test and benchmarks here for OCFS2 and NFS4. My understanding is that GFS2 limitations and performance are similar to OCFS2's, so I have not included it in the tests. My benckmarks showed that OCFS2 has an order of magnitude better performance for IMAP server (for benchmarks I have used imaptest).
Though, there are some concerns:
For better performance you would like to stick one account to one server. If one account is checked concurrently from different nodes of OCFS2 cluster they invalidates each-other the direcotory cache for the Maildir. It result in a lot more IO. I use nginx for load balancing incomming pop3/imap connections if front of dovecot servers.
OCFS2 has a limit for 32k files per directory. There is directory index support in recent kernels (> 2.6.33) that will remove this limit, but the userland tools are not yet ready for production (not in the master branch of ocfs2-tools)
My understanding is that OCFS2 uses a global lock for move/rename. As you know, Maildir format uses a lot of such operations. I think that dbox format (dovecot native) will be better choice, because there are no file moves/renames. I am planning migration to dbox now. If I have to start the service now, I would choose dbox for mail storage.
Filesystem quota. OCFS2 has support in recent kernels. It has integrated in ocfs2-tools master branch but there is not yet release of the tools. So I do not hurry to push it in production.
I hope it hepls Best regards
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