[Linux-cluster] GFS performance problem

[Riaan van Niekerk]

FM wrote:
> Thank you for the answers.
> 
> Another bottleneck that I could have is the way I connect to the SAN : 
> device mapper multipath instead of the HP officiel module.
> 
> I do not not if the performance can we increase with the official module  ?
> 

There is no SecurePath for RHEL 4 (assuming that is what you mean by 
"official module". That leaves you with
a) device-mapper-multipath
b) the Emulex or Qlogic HBA-based failover.

I have heard mostly good things about (a) even though I dont have a lot 
of production experience with it myself. It seems the trend is to move 
away from vendor/array and HBA-based multipathing towards OS-based 
multipathing, be it Windows or Linux.

> 
> 
> 
> Riaan van Niekerk wrote:
>>
>>
>> FM wrote:
>>> Hello,
>>>
>>> Here is my setup :
>>> RedHat Enterprise 4 (update 3).
>>> 5 web servers connected to a 600 GB  GFS (noatime) on a SAN.
>>> On the GFS : all web sites ROOTS and httpd logs files
>>> All web servers are writing to the same log. No problem here.
>>>
>>> The prob is with rsync. When writing on the GSF it is very very slow !
>>> (40 % slower when we are lucky :) )
>>>
>>> lots of question :
>>> *) could it be because if I have 1 GFS for the heavy write on the log
>>> and another GFS for the websites' files ?
>>> *) expect for the noatime, is there other technic to speed up GFS ?
>>
>> a) we have increased the number of GFS locks cached to bring them 
>> closer in line with the number of locks in use:
>> echo "200000" > /proc/cluster/lock_dlm/drop_count
>> (not sure how much of a performance increase this got us)
>>
>> b) We have disabled quotas
>> gfs_tool settune /mnt/san quota_account 0
>> We saw a 3 - 5 increase in performance
>>
>> c) if you are using lots of small files, look into section 5.8 in the 
>> GFS manual, Data Journaling. However,
>> - I dont know how to change this for existing data on a GFS
>> - I have asked on the mailing list, and no-one seems to be using it.
>>
>>> *) Can several webserver access EXT3 FS (read only) when only on other
>>> server have RW access to it ?
>>
>> no. the RO server will get confused when things change from under it, 
>> since it is not expecting things to change
>>
>>> *) is there a options to tune rsync when using GFS ?
>>> *) we are using DLM as the locking system. All servers are connected
>>> with Gb RJ45. Is DLM using the network to manage the lock. And if it is
>>> the case, could my problem come from the network latency ?
>>
>> DLM is using the network, yes. not sure about latency. We use GB 
>> ethernet with RJ45/CAT5+ and have not had any problems related to DLM 
>> and the network (that we are aware of). As it was explained to me by 
>> Red Hat Support, DLM is extremely efficient, being able to 
>> master/distribute thousands of locks per second between nodes.
>>
>>>
>>> As I said, lots of questions here :)
>>>
>>
>> and some answers. Wish I had answers to all your questions.
>>
>> greetings
>> Riaan
>>
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>> Linux-cluster at redhat.com
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> 
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