Hi Brendon,
I have been using iopending, though I'm not sure how to interpret it.
Is it true the column on the left is how deep in the queue requests are,
and then the histogram represents home many requests there are at each
queue depth? Then I would guess if there's lots of requests with high
queue depth, that's bad. once in awhile, I see some pretty long queues,
but they only last a second, and then things even right out again.
I'll try your disktime.d script below and the other checks you
recommend. May have more questions to follow. Thanks!
Jon
Brendan Gregg - Sun Microsystems wrote:
> G'Day Jon,
>
> For disk layer metrics, you could try Disk/iopending from the DTraceToolkit
> to check how saturated the disks become with requests (which answers that
> question with much higher definition than iostat). I'd also run disktime.d,
> which should be in the next DTraceToolkit release (it's pretty obvious),
> and is included below. disktime.d measures disk delta times - time from
> request to completion.
>
> #!/usr/sbin/dtrace -s
>
> #pragma D option quiet
> #pragma D option dynvarsize=16m
>
> BEGIN
> {
> trace("Tracing... Hit Ctrl-C to end.\n");
> }
>
> io:::start
> {
> start[args[0]->b_edev, args[0]->b_blkno] = timestamp;
> }
>
> io:::done
> /start[args[0]->b_edev, args[0]->b_blkno]/
> {
> this->delta = timestamp - start[args[0]->b_edev, args[0]->b_blkno];
> @[args[1]->dev_statname] = quantize(this->delta);
> }
>
> The iopattern script will also give you a measure of random vs sequential
> I/O - which would be interesting to see.
>
> ...
>
> For latencies in ZFS (such as ZIO pipeline latencies), we don't have a stable
> provider yet. It is possible to write fbt based scripts to do this - but
> they'll only work on a particular version of Solaris.
>
> fsinfo would be a good provider to hit up for the VFS layer.
>
> I'd also check syscall latencies - it might be too obvious, but it can be
> worth checking (eg, if you discover those long latencies are only on the
> open syscall)...
>
> Brendan
>
>
>
--
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- / / / IT Manager -
- _____ / _____ / / Space Sciences Laboratory, UC Berkeley
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