> Bit errors happen. When they do, data is corrupted. This is rather an oversimplification.
Single-bit errors *on the media* happen relatively frequently. In fact, multi-bit errors are not too uncommon either. Hence there is a lot of error-correction data written to the disc media. The error-correction codes used in disc products tend to be proprietary these days, or at least not documented. However, the error rates are published. For a typical enterprise-class disc, the correctable error rate is around 1 in 10^12 bits read, while the uncorrectable error rate is 1 in 10^15 bits read. Note that neither of these events result in data "corruption", at least in the sense of "silent data corruption", though they result in data "loss". It is possible for a pattern of bit errors to result in a miscorrection. These numbers are not published for disc drives, so far as I know. They are, however, for tape drives. A typical high-end StorageTek tape drive has an uncorrected bit error rate of 1 in 10^19 bits read, and a miscorrected bit error rate of 1 in 10^33 bits read. It seems plausible that a disc drive might have a miscorrected bit error rate, then, of no worse than 1 in 10^25 bits read. At 100 MB/second, this is roughly 3000 million years. Errors elsewhere in the system seem much more likely to introduce problems than on the media. Some low-end disks may not have any protection, or at best parity, on disk caches. The PCI bus has only parity. Both of these can be affected by double-bit errors. If you’re running on a system without ECC memory, the most likely source of undetected errors is your main memory. This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
