Re: Linux 2.6.29

Jeff Garzik
2009-03-25T21:34:17Z

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