On Tue, 16 Mar 2010, Tonmaus wrote:
None of them is active on that pool or in any existing file system. Maybe the issue is particular to RAIDZ2, which is comparably recent. On that occasion: does anybody know if ZFS reads all parities during a scrub? Wouldn't it be sufficient for stale corruption detection to read only one parity set unless an error occurs there?
Zfs scrub reads and verifies everything. That is it's purpose.
What I am trying to say is that CPU may become the bottleneck for I/O in case of parity-secured stripe sets. Mirrors and simple stripe sets have almost 0 impact on CPU. So far at least my observations. Moreover, x86 processors not optimized for that kind of work as much as i.e. an Areca controller with a dedicated XOR chip is, in its targeted field.
It would be astonishing if the XOR algorithm consumed very much CPU with modern CPUs. Zfs's own checksum is more brutal than XOR. The scrub re-assembles full (usually 128K) data blocks and verifies the zfs checksum.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
