On Aug 26, 2009, at 1:17 PM, thomas wrote:
Hi Richard,
So you have to wait for the sd (or other) driver to
timeout the request. By
default, this is on the order of minutes. Meanwhile,
ZFS is patiently awaiting a status on the request. For
enterprise class drives, there is a limited number
of retries on the disk before it reports an error.
You can expect responses of success in the order of
10 seconds or less. After the error is detected, ZFS
can do something about it.
All of this can be tuned, of course. Sometimes that
tuning is ok by default, sometimes not. Until recently, the
biggest gripes were against the iscsi client which had a
hardwired 3 minute error detection. For current
builds you can tune these things without recompiling.
-- richard
So are you suggesting that tuning the sd driver's settings to
timeout sooner if using
a consumer class drive wouldn't be wise for perhaps other reasons?
Unfortunately, it requires skill and expertise :-(. Getting it
wrong can lead to an unstable system. For this reason, the
main users of such tuning are the large integrators or IHVs.
Note: this sort of thing often does not have an immediate or
obvious impact. But it can have an impact when a failure or
unanticipated event occurs. In other words, when the going
gets tough, serviceability can be negatively impacted. Murphy's
law implies that will happen at the worst possible moment.
-- richard
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