Alan Cox wrote:
The next question is what the I/O device does with the data. SCSI disks
will cache but the scsi layer uses tags and if neccessary turns the
cache off on the drive. In other words you should get that behaviour
correctly on SCSI media.
The default IDE behaviour doesn't turn write cache off and the IDE
device may re-order writes and ack them before they hit storage. IDE
lacks tags, and tends to have poor performance on cache flush commands.
With the barrier support on the right thing should occur, or with hdparm
used to turn the write cache off.
Is this IDE behaviour confined to IDE drives only?
SATA, when using libata, will solemnly be part of the SCSI chain, and
hense not subject to your mentioned write cache problem, right?
--
Kind regards,
Mogens Valentin
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