On Tue, 11 Feb 2003 22:57, Thedore Knab wrote: > I am not talking about huge delays but rather occasional 2-5 second delays.
Have you run "iostat -x 10" or similar to see what those delays are from? > I calculate that Courier IMAP is moving about 200-500 files every minute > during the delays. > > Additionally, mail is coming in at the rate of 100-300 messages per minute. I've got ~200,000 users per server on ReiserFS and it's performing as well as can be expected. Generally performance is good enough to make everyone happy. Having >300 POP connections and >40 IMAP connections to a server at one time is not uncommon. > Since ext3 is built on top of ext2, it adds a lot of overhead. I disagree with that statement. Ext3 has been shown to increase performance over Ext2 in some situations, data=journal is the best example. Ext3 is not built on top of Ext2, it is a new file system that shares some of the same data structures as Ext2 and has backward compatability. > The kernel quotas add more overhead. Especially if they are journalled with the related meta-data changes (as is required for correct functionality). Quotas in Ext2 have traditionally been a hack and AFAIK that has not changed. The fact that quotacheck is separate from fsck is a sign of this. XFS wins in this regard, and may give you superior performance for this reason. > Since the system is not being taxed in any other noticeable way > according to sar, I feel that the file-system must be the bottleneck. > More specifically, it has to be ext3 or the quotas with ext3. Traditional sar is not much good. I recommend compiling your kernel with CONFIG_BLK_STATS and using iostat. Also does your RAID-5 have a battery backed write-back cache? This makes a huge difference to performance. Onother thing you could do is install a non-volatile RAM device such as a UMEM card for the journals and use data=journal. Then the only synchronous writes would be to a 240MB/s device with 0 latency. I've been wanting to install UMEM cards in some of my servers, from my analysis of the performance stats I expect that I could double the performance in normal operation with such hardware (cost is about $US800 for a 1G card). -- http://www.coker.com.au/selinux/ My NSA Security Enhanced Linux packages http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark http://www.coker.com.au/postal/ Postal SMTP/POP benchmark http://www.coker.com.au/~russell/ My home page -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
