> As you can see, two independent ZFS blocks share one parity block. > COW won't help you here, you would need to be sure that each ZFS > transaction goes to a different (and free) RAID5 row. > > This is I belive the main reason why poor RAID5 wasn't used in the first > place.
Exactly right. RAID-Z has different performance trade-offs than RAID-5, but the deciding factor was correctness. I'm really glad you're doing these experiments! It's good to know what the trade-offs are, performance-wise, between RAID-Z and classic RAID-5. At a minimum, it tells us what's on the table, and what we're paying for transactional semantics. To be honest, I'm pleased that it's only 2x. It wouldn't have surprised me if it were Nx for an N+1 configuration. A factor of 2 is something we can work with. Jeff _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
