[Ocfs2-users] Slow on open()

[Somsak Sriprayoonsakul]

We conducted some more tests on the SAN.

It turn out that this slow behavior only occur during the high load. Please
note that the machine is experience very high load average (50-400, we have
8 cores). Is it possible that OCFS2 server threads slowness can make the
system call stall?

We are aware of this high load problem, and we are planning to expand the
system to have more www servers in the backend. What we fear is that the
same problem will occur, or may even worse, if more servers are in the pool.

2010/1/20 Somsak Sriprayoonsakul <somsaks at gmail.com>

> No it's not cciss. This is our modprobe.conf
>
> alias eth0 bnx2
> alias eth1 bnx2
> alias scsi_hostadapter megaraid_sas
> alias scsi_hostadapter1 ata_piix
> alias scsi_hostadapter2 qla2xxx
>
> Could you suggest us how could we isolate this problem?
>
> 2010/1/20 Sunil Mushran <sunil.mushran at oracle.com>
>
> Is that using the cciss driver? I have heared of similar sporadic
>> performance
>> issues with the cciss driver. I doubt this is an ocfs2 issue. I would
>> recommend
>> you ping some support people who can look at your io setup more closely.
>>
>> Somsak Sriprayoon sakul wrote:
>>
>>> 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 <http://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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