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Re: Proposal: B_ARRIER (addresses wapbl performance?)

On Oct 29, 2008, at 2:51 PM, Thor Lancelot Simon wrote:

In practice, this would mean using an ordered tag with SCSI disks
(because ordered tags do not complete until all prior simple-tagged
commands complete)

Just because a *command* (not a *write*, necessarily) has completed doesn't mean it's on oxide. If you really want to force the simple- tagged writes before the ordered-tag write to be on oxide, your ordered-tag command should be a SYNCHRONIZE CACHE, period (and then you need to hope that your RAID vendor actually supports the command, *sigh*).

and causing a cache flush for IDE disks (at least
until we get tagged queueing support for them).  I don't know how FUA
works for IDE disks but it's been suggested to me that FUA commands
cause all pending I/O to finish before they do -- that would suffice

-- thorpej

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