It would be cool if ZFS had a layout that allowed a spare disk that was parity-only. This disk would be written-to with parity data for emergency only, and not read from. Eg. If you have a set of striped mirrors, and by some crazy chance lost both disks in a mirror...the single parity-only disk could be there to save the day. I don't believe this exists, right?
I realize it only saves the use of 1 disk, but seems like a good idea nonetheless. Would allow for very high resiliency like z2 but with simpler parity calculation which may have some advantages? The only time I tried resilvering a raidz2 pool (to upgrade disk sizes), the speed was looking so terrible that I gave up and created a new pool on the new disks and transferred over. Still a great solution for disk space utilization of course.
I realize I could create a mirrored raidz1 and then detach a disk, but wouldn't that affect write speed since all the other stripes would be reading from 2 disks and then 1 stripe would be left with only 1 disk to read? Mirrors in a stripe do increase read speed as reads are further striped, correct?
I realize it only saves the use of 1 disk, but seems like a good idea nonetheless. Would allow for very high resiliency like z2 but with simpler parity calculation which may have some advantages? The only time I tried resilvering a raidz2 pool (to upgrade disk sizes), the speed was looking so terrible that I gave up and created a new pool on the new disks and transferred over. Still a great solution for disk space utilization of course.
I realize I could create a mirrored raidz1 and then detach a disk, but wouldn't that affect write speed since all the other stripes would be reading from 2 disks and then 1 stripe would be left with only 1 disk to read? Mirrors in a stripe do increase read speed as reads are further striped, correct?