> Unfortunately there are some cases, where the disks lose data, > these cannot be detected by traditional filesystems but with ZFS: > > * bit rot: some bits on the disk gets flipped (~ 1 in 10^11) > * phantom writes: a disk 'forgets' to write data (~ 1 in 10^8) > * misdirected reads/writes: disk writes to the wrong position (~ 1 in 10^8) > > u can look up the probabilities at several disk > vendors, the are published.
I'm puzzled where you got those numbers from. They seem to be several orders of magnitude too low. Bit errors: For SATA disks, the probability of an *uncorrected* error is roughly 1 in 10^14 bits read (12 terabytes or so). [Seagate WinHEC]. These should be handled identically by ZFS and a traditional file system over RAID. The probability of either an *undetected* or *miscorrected* error is not, so far as I know, published for disks. For high-end tape, where the uncorrected error rate is roughly 1 in 10^17 bits read, the miscorrected error rate is 1 in 10^33 bits. Modern disks may use a two-level ECC [IBM ECC] which reduces even further the miscorrected error rate. These are one class of errors which ZFS will catch and a traditional file system will not. Phantom writes and/or misdirected reads/writes: I haven't seen probabilities published on this; obviously the disk vendors would claim zero, but we believe they're slightly wrong. ;-) That said, 1 in 10^8 bits would mean we’d have an error in every 12 megabytes written! That’s clearly far too low. 1 in 10^8 blocks would be an error in every 46 gigabytes written; that is also clearly far too low. (At 1 GB/second that would be a phantom write every minute.) References: [Seagate WINHEC] "SATA in the Enterprise." Can be found at <http://download.microsoft.com/download/9/8/f/98f3fe47-dfc3-4e74-92a3-088782200fe7/TWST05005_WinHEC05.ppt>. [IBM ECC] "Two-level coding for error control in magnetic disk storage products." Can be found at <http://www.research.ibm.com/journal/rd/334/ibmrd3304G.pdf>. This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
