>> 3) Try running these tests on a ccd striped over two or more identical
>> drives.
>
>   Disk /dev/rccd0a bandwidth         12138 KB/sec
>   File /n/picu/1/XXX write bandwidth: 2328 KB/sec

Many versions of the Barricuda ship with the write cache disabled since
Seagate cannot guarantee that all data in the cache will hit the disk in
the event of a loss of power.  You can enable it by tweaking mode page
8 of your drive.

As for your tagged queueing question, well, the problem is that tagged
queueing doesn't work on some devices that tell you that they support it.
Until there is a quirk assigned for this feature and the quirks list has
sufficient entries to make a high percentage of installations succeed, it
will remain a driver option.

The AHC_TAGENABLE option should be safe unless you lose power or the bus
hangs for some reason.  The reason it can be un-safe in these scenarios is
that synchronous writes can occur before the I/O that is queued before it
leading to inconsistant data if some buffers don't make it.  This problem
will be addressed, at least in FreeBSD, within the next two or three
months.

--
Justin T. Gibbs
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  FreeBSD: Turning PCs into workstations
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