> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Orvar Korvar > > I am not really worried about fragmentation. I was just wondering if I > attach new drives and zfs send recieve to a new zpool, would count as > defrag. But apparently, not.
"Apparently not in all situations" would be more appropriate. The understanding I had was: If you send a single zfs send | receive, then it does effectively get defragmented, because the receiving filesystem is going to re-layout the received filesystem, and there is nothing pre-existing to make the receiving filesystem dance around... But if you're sending some initial, plus incrementals, then you're actually repeating the same operations that probably caused the original filesystem to become fragmented in the first place. And in fact, it seems unavoidable... Suppose you have a large file, which is all sequential on disk. You make a snapshot of it. Which means all the individual blocks must not be overwritten. And then you overwrite a few bytes scattered randomly in the middle of the file. The nature of copy on write is such that of course, the latest version of the filesystem is impossible to remain contiguous. Your only choices are: To read & write copies of the whole file, including multiple copies of what didn't change, or you leave the existing data in place where it is on disk, and you instead write your new random bytes to other non-contiguous locations on disk. Hence fragmentation. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
