Christian Auby wrote: > It's not quite like copies as it's not actually a copy of the data I'm > talking about. 10% parity or even 5% could easily fix most disk errors > that won't result in a total disk loss. (snip) > I don't see a performance issue if it's not enabled by default though.
The copies code is nice because it tries to put each copy "far away" from the others. This does have a significant performance impact when on a single spindle, however, because each logical write will be written "here" and then a disk seek to write it to "there". With a N+K parity (ECC) scheme, you would turn 1 logical write into at least K disk seeks, which is by several orders of magnitude the slowest part of I/O. (unless you're using flash media, but that's not a common case yet) If you don't spread out the writes across the platter(s), you run the risk of the common-case disk failure mode where many consecutive sectors are damaged. It would not hurt when it's disabled, but it would cripple a system when it is enabled. --Joe _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
