2950 write performance issues

McDougall, Marshall (FSH) Marshall.McDougall at gov.mb.ca
Thu Jun 14 08:10:07 CDT 2007


 Thanks, Remy, but my issue is writes.

Regards, Marshall

>-----Original Message-----
>From: linux-poweredge-bounces at dell.com 
>[mailto:linux-poweredge-bounces at dell.com] On Behalf Of NOLLET 
>Remy (CAMPUS)
>Sent: Thursday, June 14, 2007 2:38 AM
>To: linux-poweredge at dell.com
>Subject: 2950 write performance issues
>
> 
>On all my PE2950, I have to change default read policy on my Raid disk.
>Please check it with "omreport storage vdisk" and change to Adaptative
>Read Ahead policy
>
>Regards
>
>Remy NOLLET
>
>
>Date: Wed, 13 Jun 2007 09:40:18 -0700
>From: Sam Flory <Sam.Flory at codegreennetworks.com>
>Subject: Re: 2950 write performance issues
>To: "McDougall, Marshall (FSH)" <Marshall.McDougall at gov.mb.ca>
>Cc: linux-poweredge at dell.com
>Message-ID: <46701DF2.5050506 at codegreennetworks.com>
>Content-Type: text/plain; charset=ISO-8859-1
>
>McDougall, Marshall (FSH) wrote:
>> 
>> I keep looking for something I can identify as the problem here.  I 
>> just noticed that memory usage is drastically different in these
>machines.
>> Outside of adjusting the shared memory for these boxes, they are the 
>> same.  Can anyone enlighten me as to why there is such a radical 
>> difference in memory usage?  What can I look at to tune?
>> 
>> Server 1 - bad:
>> [root at fsh1166db01x]# free
>>              total       used       free     shared    buffers
>> cached
>> Mem:       8310532    8294836      15696          0       6280
>> 8144720
>> -/+ buffers/cache:     143836    8166696
>> Swap:     16386292        208   16386084
>> 
>> Server 2 - good:
>> [root at fsh1166db02x]# free
>>              total       used       free     shared    buffers
>> cached
>> Mem:       8310532    2952540    5357992          0     125464
>> 2679676
>> -/+ buffers/cache:     147400    8163132
>> Swap:     16386292        208   16386084
>> 
>
>
>  The memory differences are a non issue.  The case of the 
>"good" system
>you have simply done less io.  Linux considers free memory as wasted.
>So as you read from the disk it throws everything into cache.  If you
>look at the "-/+ buffers/cache:" lines both systems have the 
>same amount
>of real world used, and free memory.  Cache pages in memory 
>are freed if
>they are needed.
>
>PS- If you run "cat /dev/sda >/dev/null" for a few seconds on 
>the "good"
>system" free should look about the same as the "bad system".
>
>
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