On Sat, Dec 19, 2009 at 7:20 PM, Bob Friesenhahn <bfrie...@simple.dallas.tx.us> wrote: > On Sat, 19 Dec 2009, Colin Raven wrote: >> >> There is no original, there is no copy. There is one block with reference >> counters. >> >> - Fred can rm his "file" (because clearly it isn't a file, it's a filename >> and that's all) >> - result: the reference count is decremented by one - the data remains on >> disk. > > While the similarity to hard links is a good analogy, there really is a > unique "file" in this case. If Fred does a 'rm' on the file then the > reference count on all the file blocks is reduced by one, and the block is > freed if the reference count goes to zero. Behavior is similar to the case > where a snapshot references the file block. If Janet updates a block in the > file, then that updated block becomes unique to her "copy" of the file (and > the reference count on the original is reduced by one) and it remains unique > unless it happens to match a block in some other existing file (or snapshot > of a file). > > When we are children, we are told that sharing is good. In the case or > references, sharing is usually good, but if there is a huge amount of > sharing, then it can take longer to delete a set of files since the mutual > references create a "hot spot" which must be updated sequentially. Files > are usually created slowly so we don't notice much impact from this sharing, > but we expect (hope) that files will be deleted almost instantaneously.
I believe this has been taken care of in space maps design (http://blogs.sun.com/bonwick/entry/space_maps provides a nice overview). Regards, Andrey > > Bob > -- > Bob Friesenhahn > bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ > GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
