linux-kernel - Re: Abysmal disk performance, how to debug?

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Date:	Sat, 20 Jan 2007 22:41:17 -0500
From:	Stephen Clark <Stephen.Clark@...lark.us>
To:	Willy Tarreau <w@....eu>
CC:	Sunil Naidu <akula2.shark@...il.com>,
	Ismail Dönmez 
	<ismail@...dus.org.tr>, linux-kernel@...r.kernel.org
Subject: Re: Abysmal disk performance, how to debug?

Willy Tarreau wrote:

>On Sat, Jan 20, 2007 at 02:56:20PM -0500, Stephen Clark wrote:
>  
>
>>Sunil Naidu wrote:
>>
>>    
>>
>>>On 1/20/07, Willy Tarreau <w@....eu> wrote:
>>>
>>>
>>>      
>>>
>>>>It is not expected to increase write performance, but it should help
>>>>you do something else during that time, or also give more responsiveness
>>>>to Ctrl-C. It is possible that you have fast and slow RAM, or that your
>>>>video card uses shared memory which slows down some parts of memory
>>>>which are not used anymore with those parameters.
>>>>  
>>>>
>>>>        
>>>>
>>>I did test some SATA drives, am getting these value for 2.6.20-rc5:-
>>>
>>>[sukhoi@...hoon ~]$ time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024
>>>1024+0 records in
>>>1024+0 records out
>>>1073741824 bytes (1.1 GB) copied, 21.0962 seconds, 50.9 MB/s
>>>
>>>What can you suggest here w.r.t my RAM & disk?
>>>
>>>
>>>
>>>      
>>>
>>>>Willy
>>>>  
>>>>
>>>>        
>>>>
>>>Thanks,
>>>
>>>~Akula2
>>>-
>>>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>>>the body of a message to majordomo@...r.kernel.org
>>>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>Please read the FAQ at  http://www.tux.org/lkml/
>>>
>>>
>>>
>>>      
>>>
>>Hi,
>>whitebook vbi s96f core 2 duo t5600 2gb hitachi ATA      HTS721060G9AT00 
>>using libata
>>time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024
>>1024+0 records in
>>1024+0 records out
>>1073741824 bytes (1.1 GB) copied, 10.0092 seconds, 107 MB/s
>>
>>real    0m10.196s
>>user    0m0.004s
>>sys     0m3.440s
>>    
>>
>
>You have too much RAM, it's possible that writes did not complete before
>the end of your measurement. Try this instead :
>
>$ time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024 | sync
>
>Willy
>
>
>  
>
Yeah that make a difference:
 time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024 | sync
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 8.86719 seconds, 121 MB/s

real    0m43.601s
user    0m0.004s
sys     0m3.912s


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