Re: True fsync() in Linux (on IDE)

[Matthias Andree <matthias.andree@gmx.de>]

Jens Axboe schrieb am 2004-03-18:

> > All these ATA fsync() vs. write cache issues have been open for much too
> > long - no reproaches, but it's a pity we haven't been able to have data
> > consistency for data bases and fast bulk writes (that need the write
> > cache without TCQ) in the same drive for so long. I have seen Linux
> > introduce TCQ for PATA early in 2.5, then drop it again. Similarly,
> > FreeBSD ventured into TCQ for ATA but appears to have dropped it again
> > as well.
> 
> That's because PATA TCQ sucks :-)

True. Few drives support it, and many of these you would not want to run
in production...

> > May I ask that the information whether a particular driver (file system,
> > hardware) supports write barriers be exposed in a standard way, for
> > instance in the Kconfig help lines?
> 
> Since reiser is the first implementation of it, it gets to chose how
> this works. Currently that's done by giving -o barrier=flush (=ordered
> used to exist as well, it will probably return - right now we just
> played with IDE).

This looks as though this was not the default and required the user to
know what he's doing. Would it be possible to choose a sane default
(like flush for ATA or ordered for SCSI when the underlying driver
supports ordered tags) and leave the user just the chance to override
this?

> Only PATA core needs to support it, not the chipset drivers. md and dm

Hum, I know the older Promise chips were blacklisted for PATA TCQ in
FreeBSD. Might "ordered" cause situations where similar things happen to
Linux?  How about SCSI/libata? Is the situation the same there?

> aren't a difficult to implement now that unplug/congestion already
> iterates the device list and I added a blkdev_issue_flush() command.

So this would - for SCSI - be an sd issue rather than a driver issue as
well?

-- 
Matthias Andree

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