Torrey McMahon wrote:
Raid calculations take CPU time but I haven't seen numbers on ZFS usage. SVM is known for using a fair bit of CPU when performing R5 calculations and I'm sure other OS have the same issue. EMC used to go around saying that offloading raid calculations to their storage arrays would increase application performance because you would free up CPU time to do other stuff. The "EMC effect" is how they used to market it.
In all modern processors, and most ancient processors, XOR takes 1 CPU cycle and is easily pipelined. Getting the data from the disk to the registers takes thousands or hundreds of thousands of CPU cycles. You will more likely feel the latency of the read-modify-write for RAID-5 than the CPU time needed for XOR. ZFS avoids the read-modify-write, but does compression, so it is possible that a few more CPU cycles will be used. But it should still be a big win because CPU cycles are less expensive than disk I/O. Meanwhile, I think we're all looking for good data on this. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
