[OmniOS-discuss] re-tune round-robin reading from a mirror

[Jim Klimov]

15 июля 2015 г. 14:10:15 CEST, Michael Mounteney <gate03 at landcroft.co.uk> пишет:
>Hello list;  is it possible with OmniOS to have a multi-way mirror with
>one disk being an SSD and the rest magnetic;  then to tune ZFS to
>perform all reads from the SSD?  for the sake of performance.  The
>default case is round-robin reading, which is the best if all disks are
>of approximately equal performance, especially if they're on separate
>controllers.  But SSD changes that.
>
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>Michael Mounteney
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When I last asked a few years ago (but IIRC forma mirror of local+iSCSI vdevs), the answer was along the lines that round-robin first considers the available devices. If the faster (ssd, local) device has no queue, it gets the load while the slower device still struggles with the task it has, so on average the faster device serves more io's - but not 100%. Queue depth tuning can also help here.

Jim

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