Re: recommended way to add ssd cache to mdraid array

[Thomas Fjellstrom <thomas@fjellstrom.ca>]

On Sun Jan 13, 2013, Chris Murphy wrote:
> On Jan 11, 2013, at 11:51 AM, Thomas Fjellstrom <thomas@fjellstrom.ca> 
wrote:
> > On Fri Jan 11, 2013, you wrote:
> >> OK fair enough, and as asked earlier, what's the chunk size?
> > 
> > Ah, sorry, I missed that bit. I didn't tweak the chunk size, so I have
> > the default 512K.
> 
> OK now that the subject has been sufficiently detoured…
> 
> Benchmarking can perhaps help you isolate causes for problems you're
> having, but you haven't said what problems you're having.  You're using
> benchmarking data to go looking for a problem. This is a GigE network to
> the NAS? If it's wireless, who cares, all of these array numbers are
> better than wireless bandwidth and latency. If it's GigE, all of your
> sequential read write numbers exceed the bandwidth of wired. So what's the
> problem? You want better random read writes? Rebuild the array with a 32KB
> or 64KB chunk size, knowing you may take a small hit on the larger
> sequential read/writes.

I did the "just ignore it" with my last array. This time around I figured it 
would be a good idea to make sure everything is setup as correctly as is 
possible given the hardware I have, because once its setup, It's too late to 
fix any issues found that need changes to the lower level settings.

To me, the write performance shown so far seems quite low, which hints at a 
problem that could be solved with some config change before I put it into 
"production". I would like to get it right (as I can), and learn a little in 
the process.

> Chris Murphy--
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-- 
Thomas Fjellstrom
thomas@fjellstrom.ca
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