Date: Fri, 7 Dec 2007 14:33:48 +0100 From: Bjorn Gronvall <bg@sics.se> To: Dag-Erling =?ISO-8859-1?Q?Sm=F8rgrav?= <des@des.no> Cc: freebsd-fs@freebsd.org Subject: Re: FSCK doesn't correct file size when INCORRECT BLOCK COUNT is found Message-ID: <20071207143348.17470be3@ibook.sics.se> In-Reply-To: <86hciuu0vn.fsf@ds4.des.no> References: <1196788555.47558b4bab0ab@imp.free.fr> <1196953310.47580ede28676@imp.free.fr> <20071206175608.594685d9@ibook.sics.se> <86hciuu0vn.fsf@ds4.des.no>
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On Fri, 07 Dec 2007 13:48:12 +0100 Dag-Erling Smørgrav <des@des.no> wrote: Hi Dag-Erling, > Bjorn Gronvall <bg@sics.se> writes: > > Filesystems in general and UFS with soft updates in particular rely on > > disks providing accurate response to writes. When write caching is > > enabled the disk will lie and tell the operating system that the write > > has completed successfully, in reality the data is only cached in disk > > RAM. When the power disappears the data will be gone forever. > > No. This used to be the case with some cheaper disks which ignored the > ATA "flush cache" command to score higher on benchmarks, but I doubt > you'll find any disks on the market that still do that (at least from > reputable manufacturers). Agreed, but the software must also be written to actually make use of the more recent "flush cache" feature. I know that the GEOM journal can make use of this feature but does UFS with soft updates use it? > ZFS makes extensive use of the "flush cache" > command to ensure file system integrity (and in particular to ensure > that the intent log is written to disk so it can be replayed in case of > a crash). ZFS is a more recent beast than UFS and was probably designed with the "flush cache" feature in mind right from the very beginning. Cheers, /b -- _ _ ,_______________. Bjorn Gronvall (Björn Grönvall) /_______________/| Swedish Institute of Computer Science | || PO Box 1263, S-164 29 Kista, Sweden | Schroedingers || Email: bg@sics.se, Phone +46 -8 633 15 25 | Cat |/ Cellular +46 -70 768 06 35, Fax +46 -8 751 72 30 '---------------'
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