On Tue, Jan 30, 2007 at 06:32:14PM +0100, Roch - PAE wrote: > > The only benefit of using a HW RAID controller with ZFS is that it > > reduces the I/O that the host needs to do, but the trade off is that ZFS > > cannot do combinatorial parity reconstruction so that it could only > > detect errors, not correct them. It would be cool if the host could > > offload the RAID I/O to a HW controller but still be able to read the > > individual stripes to perform combinatorial parity reconstruction. > > right but in this situation, if the "cosmic ray / bit flip" hits on the > way to the controller, the array will store wrong data and > we will not be able to reconstruct the correct block. > > So having multiple I/Os here improves the time to data > loss metric.
You missed my point. Assume _new_ RAID HW that allows the host to read the individual stripes. The ZFS could offload I/O to the RAID HW but, when a checksum fails to validate on read, THEN go read the individual stripes and parity and do the combinatorial reconstruction as if the RAID HW didn't exist. I don't believe such RAID HW exists, therefore the point is moot. But if such HW ever comes along... Nico -- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
