On Mar 14, 2010, at 11:45 AM, Tonmaus wrote: > Hi Richard, > > thanks for the answer. I think I am aware on the properties of my > configuration and how it will scale. Let me please stress that this is not > the point in the discussion. > The target of this discussion should rather be if scrubbing can co-exist with > payload or if we are thrown back to scrub in the after-hours. > So, do I have to conclude that zfs is not able to make good decisions about > load prioritisation on commodity hardware and that there are no further > options available to tweak scrub load impact, or are there other options?
ZFS prioritizes I/O. Scrub has the lowest priority. The scrub will queue no more than 10 I/Os at one time to a device, so devices which can handle concurrent I/O are not consumed entirely by scrub I/O. This could be tuned lower, but your storage is slow and *any* I/O activity will be noticed. > I am thinking about managing pools capable of hundred times the capacity of > mine (currently there are 3,7 TB on disk, and it takes 2,5 h to scrub them on > the double-parity pool) that practically would be un-scrub-able. (Yes, > Enterprise HW is faster, but Enterprise service windows are much more narrow > as well... you can't move around or offline 200 TB of live data for days only > because you need to scrub the disks can you?) I can't follow your logic here. Scrub is a low priority process and should be done at infrequent intervals. If you are concerned that a single 200TB pool would take a long time to scrub, then use more pools and scrub in parallel. > The only idea I could think of myself is to exchange individual drives in a > round-robin fashion all the time and use re-silver instead of full scrubs. > But actually I don't like the idea anymore at second glance. You are right, this would not be a good idea. -- richard ZFS storage and performance consulting at http://www.RichardElling.com ZFS training on deduplication, NexentaStor, and NAS performance Atlanta, March 16-18, 2010 http://nexenta-atlanta.eventbrite.com Las Vegas, April 29-30, 2010 http://nexenta-vegas.eventbrite.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
