On Fri, January 8, 2010 07:51, Robert Milkowski wrote: > On 08/01/2010 12:40, Peter van Gemert wrote: >>> By having a snapshot you >>> are not releasing the >>> space forcing zfs to allocate new space from other >>> parts of a disk >>> drive. This may lead (depending on workload) to more >>> fragmentation, less >>> localized data (more and longer seeks). >>> >>> >> ZFS uses COW (copy on write) during writes. This means that it first has >> to find a new location for the data and when this data is written, the >> original block is released. When using snapshots, the original block is >> not released. >> >> I don't think the use of snapshots will alter the way data is fragmented >> or localized on disk.
> Well, it will (depending on workload). > For example - lets say you have a 80GB disk drive as a pool with a > single db file which is 1GB in size. > Now no snapshots are created and you constantly are modyfing logical > blocks in the file. As ZFS will release the old block and will re-use it > later on so all current data should be roughly within the first 2GB of > the disk drive therefore highly localized. I thought block re-use was delayed to allow for TXG rollback, though? They'll certainly get reused eventually, but I think they get reused later rather than sooner. -- David Dyer-Bennet, d...@dd-b.net; http://dd-b.net/ Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/ Photos: http://dd-b.net/photography/gallery/ Dragaera: http://dragaera.info _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
