Peter Jeremy peterjeremy at optushome.com.au
Sat Sep 27 07:36:22 UTC 2008

On 2008-Sep-26 23:44:17 -0700, Jeremy Chadwick <koitsu at freebsd.org> wrote:
>On Fri, Sep 26, 2008 at 10:35:57PM -0700, Derek Kuli??ski wrote:
>> As far as I know (at least ideally, when write caching is disabled)
>FreeBSD atacontrol does not let you toggle such features (although "cap"
>will show you if feature is available and if it's enabled or not).

True but it can be disabled via the loader tunable hw.ata.wc (at
least in theory - apparently some drives don't obey the cache disable
command to make them look better in benchmarks).

>Users using SCSI will most definitely have the ability to disable
>said feature (either via SCSI BIOS or via camcontrol).

Soft-updates plus write caching isn't an issue with tagged queueing
(which is standard for SCSI) because the critical point for
soft-updates is knowing when the data is written to non-volatile
storage - which tagged queuing provides.

Peter Jeremy
Please excuse any delays as the result of my ISP's inability to implement
an MTA that is either RFC2821-compliant or matches their claimed behaviour.
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