HAST performance / dtrace / _umtx_op

[Ivan Voras]

On 26/04/2014 12:30, Karl Pielorz wrote:
> 
> Hi All,
> 
> I've been looking at HAST recently - and noticed there's a huge
> performance hit (on 10-STABLE anyway) even if you setup a disk with a
> remote of 'none' - switching from the 'raw' disk to '/dev/hast/disk'
> shows a 50% performance hit [in testing having an active secondary via
> 10Gbit link doesn't seem to show any further performance drop].

HAST is a GEOM_GATE solution so every IO request goes through a
round-trip to the userland hastd process. This could be one of the
reasons for the slowness. IIRC it is still async, so adding the second
remote note would not slow it down additionally since it doesn't wait
for the network request.

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