On Mar 21, 2011, at 5:09 AM, Edward Ned Harvey wrote: >> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- >> boun...@opensolaris.org] On Behalf Of Richard Elling >> >> How many times do we have to rehash this? The speed of resilver is >> dependent on the amount of data, the distribution of data on the > resilvering >> device, speed of the resilvering device, and the throttle. It is NOT > dependent >> on the number of drives in the vdev. > > What the heck? Yes it is. Indirectly. When you say it depends on the > amount of data, speed of resilvering device, etc, what you really mean > (correctly) is that it depends on the total number of used blocks that must > be resilvered on the resilvering device, multiplied by the access time for > the resilvering device. And of course, throttling and usage during resilver > can have a big impact. And various other factors. But the controllable big > factor is the number of blocks used in the degraded vdev.
There is no direct correlation between the number of blocks and resilver time. > So here is how the number of devices in the vdev matter: > > If you have your whole pool made of one vdev, then every block in the pool > will be on the resilvering device. You must spend time resilvering every > single block in the whole pool. > > If you have the same amount of data, on a pool broken into N smaller vdev's, > then approximately speaking, 1/N of the blocks in the pool must be > resilvered on the resilvering vdev. And therefore the resilver goes > approximately N times faster. Nope. The resilver time is dependent on the speed of the resilvering disk. > So if you assume the size of the pool or the number of total disks is a > given, determined by outside constraints and design requirements, and then > you faced the decision of how to architect the vdev's in your pool, then > Yes. The number of devices in a vdev do dramatically impact the resilver > time. Only because the number of blocks written in each vdev depend on > these decisions you made earlier. I do not think it is wise to set the vdev configuration based on a model for resilver time. Choose the configuration to get the best data protection. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
