> From: edmud...@mail.bounceswoosh.org > [mailto:edmud...@mail.bounceswoosh.org] On Behalf Of Eric D. Mudama > > On Mon, Dec 20 at 19:19, Edward Ned Harvey wrote: > >If there is no correlation between on-disk order of blocks for different > >disks within the same vdev, then all hope is lost; it's essentially > >impossible to optimize the resilver/scrub order unless the on-disk order of > >multiple disks is highly correlated or equal by definition. > > Very little is impossible. > > Drives have been optimally ordering seeks for 35+ years. I'm guessing
Unless your drive is able to queue up a request to read every single used part of the drive... Which is larger than the command queue for any reasonable drive in the world... The point is, in order to be "optimal" you have to eliminate all those seeks, and perform sequential reads only. The only seeks you should do are to skip over unused space. If you're able to sequentially read the whole drive, skipping all the unused space, then you're guaranteed to complete faster (or equal) than either (a) sequentially reading the whole drive, or (b) seeking all over the drive to read the used parts in random order. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
