vinum performance

[Jason Andresen]

Greg 'groggy' Lehey wrote:

>>>>I get 4565 K/sec on modern ATA/133 HDDs.
>>>>
>>>>Reading is much better at 91908 K/sec at least.
>>
>>Well, I'm writing 200MB files most of the time, so the stripe size is
>>not an issue.  I'm just wondering why the reads are *20* times faster
>>than the writes.
> 
> 
> They're not.  I don't know where you get that read figure from, but no
> disk can transfer that fast, and you don't appear to be doing multiple
> transfers in parallel.

That was what bonnie++ reported.

>>I think the read performance was CPU limited in this case.
> 
> 
> I think you were reading from cache.

Quite possible.  I'm not sure how bonnie handles that.

>>While some of this is probably an oddity with bonnie (Bonnie always
>>reports my writes to be about half as fast as the reads, but dd
>>thinks otherwise:
>>
>>(Both of these were on previously untouched files to prevent any
>>caching, and the "write" test is on a new file, not rewriting an old one)
>>Write speed:
>>81920000 bytes transferred in 3.761307 secs (21779663 bytes/sec)
>>Read speed:
>>81920000 bytes transferred in 3.488978 secs (23479655 bytes/sec)
>>
>>But on the RAID5:
>>Write speed:
>>81920000 bytes transferred in 17.651300 secs (4641018 bytes/sec)
>>Read speed:
>>81920000 bytes transferred in 4.304083 secs (19033090 bytes/sec)
> 
> 
> Yes, this is very close to the 4:1 ratio that I would expect.  If
> you're looking for write performance, don't use RAID-5.

So FreeBSD never optimizes out those first two operations?  I was 
thinking writing fresh large files to a RAID5 array would only be half 
as fast as reading.

-- 
   \  |_ _|__ __|_ \ __| Jason Andresen        jandrese at mitre.org
  |\/ |  |    |    / _|  Network and Distributed Systems Engineer
_|  _|___|  _| _|_\___| Office: 703-883-7755