[Ocfs2-users] Slow on open()

[Somsak Sriprayoonsakul]

Hello,

We are using OCFS2 version 1.4.3 on CentOS5, x86_64 with 8GB memory. The
underlying storage is HP 2312fc smart array equipped with 12 SAS 15K rpm,
configured as RAID10 using 10 HDDs + 2 spares. The array has about 4GB
cache. Communication is 4Gbps FC, through HP StorageWorks 8/8 Base e-port
SAN Switch. Right now we only have this machine connect to the SAN through
switch, but we plan to add more machine to utilize this SAN system.

Our application is apache version 1.3.41, mostly serving static HTML file +
few PHP. Note that, we have to downgrade to 1.3.41 due to our application
requirement. Apache is configured on has 500 MaxClients.

The storage OCFS2 are formatted with mkfs.ocfs2 without any special option
on. It run directly from multipath'ed SAN storage without LVM or software
RAID. We mount OCFS2 with noatime, commit=15, and data=writeback (as well as
heartbeat=local). Our cluster.conf is like this

cluster:
    node_count = 1
    name = mycluster

node:
    ip_port = 7777
    ip_address = 203.123.123.123
    number = 1
    name = mycluster.mydomain.com
    cluster = mycluster

(NOTE: Some details are neglected here, such as hostname and IP address).

Periodically, we found that the file system work very slow. I think that it
happened once every few minutes. When the file system slow, httpd process
CPU utilization will goes much higher to about 50% or above. I tried to
debug this slow by creating a small script that periodically do

strace -f dd if=/dev/zero of=/san/testfile bs=1k count=1

And time the speed of dd, usually dd will finish within subsecond, but
periodically dd will be much slower to about 30-60 seconds. Strace output
show this.

     0.000026 open("/san/testfile", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 1
    76.418696 rt_sigaction(SIGUSR1, NULL, {SIG_DFL, [], 0}, 8) = 0

So I presume that this mean the open system call is periodically very slow.
I did about 5-10 tests which yield similar strace'd results (ranging from
just 5-7 seconds to 80 seconds).

So my question is, what could be the cause of this slowness? How could I
debug this deeper? On which point should we optimize the file system?

We are in the process of purchasing and adding more web servers to the
system and use reverse proxy to load balance between two servers. We just
want to make sure that this will not make situation worst.
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