[wplug] Hardware RAID tuning

[Matthew Zwier]

And by PCI I mean PCI Express.

On Thu, Jun 16, 2011 at 11:00 AM, Matthew Zwier <mczwier at gmail.com> wrote:
> On Wed, Jun 15, 2011 at 10:17 PM, Drew from Zhrodague
> <drewzhrodague at zhrodague.net> wrote:
>>        Shouldn't you not share controllers with other arrays, and actually use
>> multiple controllers per array? This is how we did things back in the
>> day with old JBOD Suns -- stripe across disks and stripe across
>> controllers. Modern architectures turn everything on their ears, so I
>> could be missing something.
>
> I doubt you're missing something, but we're out of slots in the
> server, and out of space in the rack for a new one :)  Did I mention
> this is a scientific computing cluster for a small research group?
> Funds and space are limited.  Also, I can't correlate the performance
> drop to a specific load on the other array.
>
>>        If it helps, I've found that a straight scp in Amazon's cloud is faster
>> than an scp -C or compressed rsync. The results may be different with a
>> hardware environment, but testing is the only way to be sure.
>
> Yeah, tested this yesterday.  Compression slows things down
> considerably, Enumerating files (rsync) slows things down to kilobytes
> per second.  A typical user has a million or so tiny files and a few
> hundred (10 GB - 200 GB) very large files.  xfsdump over an
> uncompressed ssh connection appears the way to go.
>
> Interestingly, piping things through bar to measure throughput seems
> to slow things down a *lot*, and in fact may be the greater reason for
> the intermittent throughput -- I'm sustaining 4 MB/s - 50 MB/s,
> seemingly correlated to what set of files xfsdump is working on, now
> that I don't have bar in the pipe.  I'm wondering if I need to do
> something *really* dumb, like xfsdump -J - | xfsrestore -J -
> /some/nfs/mount.  That would seem to be going through one fewer
> userland buffers.
>
> Hmm...what's the bandwidth of a PCI bus?
>
> MZ
>