On Fri, Jan 26, 2007 at 11:05:17AM -0800, Ed Gould wrote: > > A number that I've been quoting, albeit without a good reference, comes > from Jim Gray, who has been around the data-management industry for > longer than I have (and I've been in this business since 1970); he's > currently at Microsoft. Jim says that the controller/drive subsystem > writes data to the wrong sector of the drive without notice about once > per drive per year. In a 400-drive array, that's once a day. ZFS will > detect this error when the file is read (one of the blocks' checksum > will not match). But it can only correct the error if it manages the > redundancy.
My only qualification to enter this discussion is that I once wrote a floppy disk format program for minix. I recollect, however, that each sector on the disk is accompanied by a block that contains the sector address and a CRC. In order to write to the wrong sector, both of these items would have to be read incorrectly. Otherwise, the controller would never find the wrong sector. Are we just talking about a CRC failure here? That would be random, but the frequency of CRC errors would depend on the signal quality. -- -Gary Mills- -Unix Support- -U of M Academic Computing and Networking- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
