Are large RAID stripe sizes useful with FreeBSD?
ivoras at freebsd.org
Mon Mar 31 14:34:09 PDT 2008
On 31/03/2008, Scott Long <scottl at samsco.org> wrote:
> For writes, the performance penalty of smaller I/O's (assuming no RAID-5
> effects) is minimal; most caching controllers and drives will batch the
> concurrent requests together, so the only loss is in the slight overhead
> of the extra transaction setup and completion. For reads, the penalty
> can be greater because the controller/disk will try to execute the first
> request immediately and not wait for the second part to be requested,
> leading to the potential for extra rotational and head movement delays.
> Many caching RAID controllers offer a read-ahead feature to counteract
> this. However, while my testing has shown little measurable benefit to
> this, YMMV.
Thank you, this is the kind of explanation I hoping for. One more
thing: is TCQ (e.g. the SCSI variant) orthogonal to this?
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