Re: safe file systems

Doug Ledford (
Wed, 24 Sep 1997 22:36:36 -0500

> > Also, your writes have to be very strictly ordered. Some intelligent IO
> > subsystems will reorder your write operations on you, which I guess could
> > cause lots of really obscure hard to track down funnies if you were unaware
> > of you IO doing this.
> SCSI itself has flags to stop that happening. We don't appear to have any way
> right now to mark a request ordered let alone tell the scsi layer to tell
> the card to order it.

IDE doesn't have this problem as long as there is no write cacheing enabled
on the drive itseslf. SCSI can get around the problem by disabling tagged
queueing (as an immediate fix), or by adding an ordered tag flag for
commands on tagged queueing devices. However, to truly gaurantee ordered
writes on SCSI you would have to disable drive write cacheing here as well.

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