On 11/1/07, Nathan Kroenert <[EMAIL PROTECTED]> wrote:
> Tell me - If you watch with an iostat -x 1, do you see bursts of I/O
> then periods of nothing, or just a slow stream of data?
>
> I was seeing intermittent stoppages in I/O, with bursts of data on
> occasion...
I have seen this with ZFS under 10U3, both SPARC and x86,
although the cycle rate differed. Basically, no i/o reported via zpool
iostat 1 or iostat -xn 1 (to the raw devices) for a period of time
followed by a second of ramp up, one or more seconds of excellent
throughput (given the underlying disk systems), a second of slow down,
then more samples with no i/o. The period between peaks was 10 seconds
in one case and 7 in the other. I forget which was SPARC and which was
x86.
I assumed this had to do with ZFS caching i/o until it had a
large enough block to be worth writing. In some cases the data was
coming in via the network (NFS in one SMB in the other), but in
neither case was the network interface saturated (in fact, I saw
similar periods of no activity on the network) and the did not seem to
be a CPU limitation (load was low and idle time high). I have also
seen this with local disk to disk copies (from UFS to ZFS or ZFS to
ZFS).
--
Paul Kraus
Albacon 2008 Facilities
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