Re: xfs vs jfs performance
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).
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