Kenny:
Performance is all about your application; it's response time, throughput,
and variance in those metrics. I suggest that all your problem-solving
start
and end from that perspective. If your application performance is not what
you need and you suspect ZFS is the reason, there are tools to investigate
any hypothesis you can conceive. Targeted advice would require knowing
the details of your application and your performance requirements.
Though ZFS was designed to be extremely simple to use, some tuning may
be required to make it work for your application. Check out the "ZFS Evil
Tuning Guide" for guidance.
The features of ZFS come at a cost, and those costs sometimes mean that
ZFS will not meet some performance requirements. For example, if your
random reads are slowed down too much by ZFS reading whole ZFS
records - especially if you have a very sparse locality of reference - you
would have to reduce the ZFS recordsize to counter. However, reducing
the recordsize can cause sequential reads to require more I/O operations as
copy-on-write file updating makes the data less contiguous on disk. This
recordsize tradeoff is among the fundamental and immutable tradeoffs in
deploying ZFS.
Random writes with ZFS can require Read/Modify/Write I/O patterns
when the write size is less than a ZFS record and the containing ZFS record
is not already in memory. This can lead to a severe application-perceived
inflation of write latency for synchronous random writes.
Other potential issues may arise from the memory usage patterns of ZFS
or its CPU requirements relative to other options. Whether or not any of
these is limiting is entirely specific to the case at hand.
Cheers,
-- Bob
kenny wrote:
hello all,
i was wondering what is the recommended way to measure the performance of zfs.
i think my performance isn't as good as it should be, but with no measurement, i don't even know is my assumption is correct or wrong.
so what do people around here use to measure zfs performance?
thanks
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