> But note that, for ZFS, the win with direct I/O will be somewhat > less. That's because you still need to read the page to compute > its checksum. So for direct I/O with ZFS (with checksums enabled), > the cost is W:LPS, R:2*LPS. Is saving one page of writes enough to > make a difference? Possibly not.
It's more complicated than that. The kernel would be verifying checksums on buffers in a user's address space. For this to work, we have to map these buffers into the kernel and simultaneously arrange for these pages to be protected from other threads in the user's address space. We discussed some of the VM gymnastics required to properly implement this back in January: http://mail.opensolaris.org/pipermail/zfs-discuss/2007-January/thread.html#36890 -j _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
