Re: Linux 2.6.29

[Jeff Garzik]

Linus Torvalds wrote:
> OS X, for example, doesn't do the disk barrier. It requires you to do a 
> separate FULL_FSYNC (or something similar) ioctl to get that. Apparently 
> exactly because users don't expect quite _that_ big of a performance hit.

I can understand that, more from an admin standpoint than anything... 
ATA disks' FLUSH CACHE is horribly coarse-grained, all-or-nothing.

SCSI's SYNCHRONIZE CACHE at least gives us an optional (LBA, length) 
pair that can be used to avoid to flushing everything in the cache.

Microsoft has publicly proposed a WRITE BARRIER command for ATA, to try 
and improve the situation:
http://www.t13.org/Documents/UploadedDocuments/docs2007/e07174r0-Write_Barrier_Command_Proposal.doc

but that isn't in the field yet (if ever?)

	Jeff


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