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Re: LVM negates benefits of jounaling filesystems? [was RFE: autofsck]



On Tue, Jun 10, 2008 at 09:05:34AM -0500, Eric Sandeen wrote:
> Barriers do have performance impact, which is probably historically why
> they're off by default on ext3.  I'm not totally convinced that it's a

The cost is dropping rapidly with SATA devices. With a modern SATA disk and
NCQ we really really want them on - you've got 31 commands in flight and 16MB
or so of drive cache that will be written back in *arbitary* order. Thats
a recipe for disaster. A few years ago with one command at a time wind up
disks and at most 2MB it wasn't so bad. It really should be getting set on by
either our kernel or the installer in the SATA cases.

Alan


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