Re: Slow writing speed on LTO4 SAS tape

2010/2/25 Silviu Marin-Caea <[email protected]>:
> On Wed, 24 Feb 2010 16:08 -0300, "Ciro Iriarte" <[email protected]>
> wrote:
>
>> Hmmm, just to make sure, do a test reading from memory.
>>
>> dd if=/dev/zero of=/dev/st0
>
> time dd if=/dev/zero of=/dev/nst0 bs=1M count=4096
> 4096+0 records in
> 4096+0 records out
>
> real    0m26.642s
> user    0m0.002s
> sys     0m1.245s
>
> Would that be relevant?  The drives have hardware compression activated.
>  So this command would show just how fast the drive can compress a
> stream of zero and write to tape much less actual data than 4GB.
>
> The speed computes to around 157 MB/s, the device specification is 120
> MB/s
>
> Is this rationale correct?  Am I missing something?

Disabling the compression would make sense. That way you can test raw
performance without being dragged down by the array (in case it's the
bottleneck in your case).

Regards,

-- 
Ciro Iriarte
http://cyruspy.wordpress.com
--
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