Currently, the algorithm is approximately round-robin. We try to keep all vdevs working at all times, with a slight bias towards those with less capacity. So if you add a new disk to a pool whose vdevs are 70% full, we'll gradually schedule more work for the empty disk until all the vdevs are again even.
This algorithm leaves a lot to be desired when there is one or more disks misbehaving in a non-fatal manner. Currently, if you have a single vdev which is slower than the rest, it will slow down operation of the entire pool. This includes a failing device, which continues to respond to requests, albeit very slowly. We have ideas for improvement in this area, but have been preoccupied with some of the lower-hanging performance wins. Eventually, we'll want to take a number of factors into account, including capacity, latency, past errors, etc. - Eric On Tue, Jul 18, 2006 at 08:49:28AM -0400, David Blacklock wrote: > Hello, > > What is the access algorithm used within multi-component pools for a > given pool, and does it change when one or more members of the pool > become degraded ? > > examples: > > zpool create mtank mirror c1t0d0 c2t0d0 mirror c3t0d0 c4t0d0 mirror > c5t0d0 c6t0d0 > > or; > > zpool create ztank raidz c1t0d0 c2t0d0 c3t0d0 raidz c4t0d0 c5t0d0 c6t0d0 > > As files are created on the filesystem within these pools, are they > distributed round-robin accross the components, or do they stay with the > first component till full then go to the next, or is some other > technique used ? > > Then, when a component becomes degraded, c1t0d0 for example, are new > files still created on the degraded component, or is that component > skipped until no longer degraded or until it is needed; i.e. you run out > of space on the other components that have good status ? > > -thanks, > -Dave > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss -- Eric Schrock, Solaris Kernel Development http://blogs.sun.com/eschrock _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
