Re: Linux 2.6.29
From: Jeff Garzik
Date: Wed Mar 25 2009 - 17:34:18 EST
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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