Dell Poweredge 2950 with PERC 5/i RAID

[Johan De Meersman]

Giulio Orsero wrote:
> On 10/9/06, Claudio Nasuti <claudio.nasuti at acsys.it> wrote:
>   
>> The installation went smooth like a breeze but when I made a small IO test I have been shocked
>> IO seems very poor as everyone can figure by numbers
>> [root at adm-sdf1 ~]# time dd if=/dev/zero of=./DummyFile bs=65536 count=65536
>> 65536+0 records in
>> 65536+0 records out
>>
>> real    1m49.236s
>>     
>
> If I'm not mistaken the test shows you get about 37MB/s.
> If this is very poor, what numbers did you expect?
>   

Considering I'd expect somewhere between 50 and 70 MB/s sequential write
throughput on servers with 72G 15krpm disks in raid 5, I think this is
reasonable, considering the slower and larger disks.

Just did the same test on a 4 year old system, and I got about 45MB/s.

Remember that write throughput depends on rotation speed, number of
spindles and stripe size - if your stripe size is identical to your
transaction size, every transaction will be handled by a different
spindle of the disk array, optimizing parallelism.

If you're running 2.6 series, you can also have a look at using the
deadline I/O scheduler instead of the standard (anticipatory) one -
anticipatory assumes only a single spindle, while deadline can take
advantage of command tagging and queueing. YMMV.




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