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From "B. Todd Burruss" <bburr...@real.com>
Subject Re: Read Latency
Date Tue, 11 May 2010 16:10:15 GMT
you can try this benchmarking tool to compare your drive(s)

http://freshmeat.net/projects/fio/

... you can simulate various loads, etc.  my RAID0 outperforms single 
drive (as mentioned below) under heavy concurrent reads.

On 05/11/2010 08:15 AM, Peter Schüller wrote:
>> isolated requests, obviously in scale the RAID should perform better... I
>> have not started testing concurrent reads in scale as the single reads are
>> too slow to begin with. I am getting 20-30ms response time off of internal
>>      
> Concurrent reads is what you need to do in order to see the benefit of
> a RAID controller with many constituent drives under it.
>
>    
>> drives and 50-70 ms response time through the raid volumes (as reported in
>> cfstats). The system is totally idle and all data has been cleanly
>>      
> That said, a RAID controller imposing several tens of extra
> milliseconds of latency sounds strange; something else or fishy has to
> be going on.
>
> But don't expect sequential reads of non-cached small random-access
> data to be faster with a RAID controller. The benefit of RAID will
> tend to be overall throughput when doing concurrent reads, fast
> fsync() (low latency on durable writes) and the ability to eat bursts
> of write activity in battery backed cache.
>
>    

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