Hi Gabor,

On Thu, Nov 27, 2008 at 12:47:48PM +0100, Gabor Gombas wrote:

Are these values useful for mere mortals trying to create a RAID array
best suited for a specific workload, or are these only useful for people
hacking on the RAID code?

I believe the average administrator could understand what most (if not
all) of the statistics mean, but doing something about it might require
a developer or at least someone with a bit of RAID experience.  In our
use, we get customers to report the values to us then make tuning
suggestions (more likely) or provide a patch.

If the former, then I'd suggest to use sysfs (something like
/sys/block/<dev>/md/statistics, similar to
/sys/class/net/<dev>/statistics). If the latter, then debugfs would be
better.

I was thinking about your first suggestion but note that there is also
/proc/diskstats as well as /sys/block/<dev>/stat.  The advantage of
having everything in one file is that you only have to open one file
when gathering statistics on many arrays, and /proc/mdstat already
exists as a precedent.  I could add individual array statistics files as
well if useful.

I'm also going to investigate tracepoints as suggested by Dan, so all
this is subject to change :)

Cheers,
Jody

Gabor

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     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
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