On Tue, Apr 26, 2005 at 02:30:12PM +1000, Benjamin Herrenschmidt wrote:
> Additionally, some machines won't properly park/flush the disk, it's
> necessary to send the proper suspend commands to IDE hard disks prior to
> shutting down or we risk data loss.
That sounds like the disk is caching write data.
SCSI has a "Write Cache Enable" bit in the "caching mode page".
See "scsiinfo -c" output.
10 years ago I measured/compared performance of disabling WCE
(plus queue depth of 8) and enabling WCE (queue depth 1).
It's a wash for the workloads I was testing. I was told "stupid OSs"
that didn't know about tagged queueing needed WCE for benchmarks.
HP cared for exactly the same reasons: Bus Resets or Disk power failure
would cause data loss with WCE enabled.
Disabling WCE on current OSs would solve the above problem
IFF IDE/SATA also supports "cache mode" page.
grant
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