Re: SATA-performance: Linux vs. FreeBSD

[Alan]

> there's several tunables you can do;
> 1) increase /sys/block/<device>/queue/nr_requests
>    the linux default is on the low side
> 5) echo a larger value into /sys/block/<device>/queue/max_sectors_kb
>    the default seems to be 512 which is... really low. The hw max is in
>    another file in that directory; if you want max throughput set the
>    max_sectors_kb value to the hw max. (you pay in terms of fairness for


There are two more factors that play into #1 and #5. Firstly there is a
per command completion overhead in ATA without NCQ being active and that
isn't yet a heavily optimised libata path. Secondly erase block size
matters with flash drives so the bigger each I/O the better erase block
behaviour we should get.
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