Le 28 févr. 08 à 21:00, Jonathan Loran a écrit : > > > Roch Bourbonnais wrote: >> >> Le 28 févr. 08 à 20:14, Jonathan Loran a écrit : >> >>> >>> Quick question: >>> >>> If I create a ZFS mirrored pool, will the read performance get a >>> boost? >>> In other words, will the data/parity be read round robin between the >>> disks, or do both mirrored sets of data and parity get read off of >>> both >>> disks? The latter case would have a CPU expense, so I would think >>> you >>> would see a slow down. >>> >> >> 2 disks mirrored together can read data faster than a single disk. >> So to service a read only one side of the mirror is read. >> >> Raid-Z parity is only read in the presence of checksum errors. > That's what I suspected, but I'm glad to get the final word on > this. BTW, I guess I should have said checksums instead of parity. > My bad. >
OK. The checksum is a different story and is stored within the metadata block pointing to the data block. So given that to reach the data block we've already had to read the metadata block, checskum validation is never the source of an I/O. > Thanks, > > Jon > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
