> 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. 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. 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. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
