Date: Fri, 9 Jun 2006 19:59:23 +1000 From: Peter Jeremy <peterjeremy@optushome.com.au> To: "Daniel O'Connor" <doconnor@gsoft.com.au> Cc: freebsd-current@freebsd.org Subject: Re: Data authentication for geli(8) committed to HEAD. Message-ID: <20060609095923.GB739@turion.vk2pj.dyndns.org> In-Reply-To: <200606091215.41787.doconnor@gsoft.com.au> References: <20060608132048.GD86198@garage.freebsd.pl> <20060608174113.GC1075@roadrunner.q.local> <200606091215.41787.doconnor@gsoft.com.au>
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--3lcZGd9BuhuYXNfi Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, 2006-Jun-09 12:15:33 +0930, Daniel O'Connor wrote: >I think that in reality with a modern high capacity disk you don't get ato= mic=20 >writes at all because they all re-write whole tracks. AFAIK, this applies to _all_ modern disks, whether they're SATA, PATA or SC= SI. >Yes this violates the assumption soft updates makes, I believe the only wa= y=20 >around it is to buy SCSI drives (not because they're SCSI per se, but beca= use=20 >they're smaller capacity so they don't do this) Not totally. Soft updates requires that the device driver inform the filesystem when a write has been committed to non-volatile media. The device driver can only do this if the underlying device reports this. All SCSI devices do but few ATA devices support tagged queueing so the device driver can only tell that the data has been written to the disk cache, not that the data has been committed. You can work around this (at the cost of reducing write performance by about an order of magnitude) by disabling write caching. --=20 Peter Jeremy --3lcZGd9BuhuYXNfi Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (FreeBSD) iD8DBQFEiUZ3/opHv/APuIcRAlDXAJ92h716J2xAq23+Qf7qz2kjY2UMnACffmC0 kikRsuEcBVIehGCqechqXHM= =BdHB -----END PGP SIGNATURE----- --3lcZGd9BuhuYXNfi--
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