Hi, We''re currently testing a Thumper running Solaris10 with a view to buying a couple. I''m not seeing what I would expect to see as far as snapshot space utilization and am hoping someone could explain why. Here''s what I''m doing - Creating an empty zpool & zfs Creating a 6MB text file Taking a snapshot So far so good. The filesystem size is 6MB and the snapshot 0MB Now I edit the first 4 characters of the text file. I would have expected the size of the snapshot to have grown by the size of the changed *blocks* but when I do a ''zfs list'' the filesystem is now reported as being around 12MB total with the snapshot around 6MB. So the snapshot is being reported as being the size of the changed *files* and not the changed *blocks*. Is this corret (that the snapshot is consuming this space) or is that just how it''s being reported with th zfs list command? Many thanks - Matt This message posted from opensolaris.org
How are you editing the file? Are you sure your editor isn''t writing out the entire file even though only four characters have changed? If you truss the app, do you see a single 4 byte write to the file? - Eric On Wed, Jan 23, 2008 at 11:11:38AM -0800, Matt Newcombe wrote:> Hi, > > We''re currently testing a Thumper running Solaris10 with a view to buying a couple. > > I''m not seeing what I would expect to see as far as snapshot space utilization and am hoping someone could explain why. > > Here''s what I''m doing - > > Creating an empty zpool & zfs > Creating a 6MB text file > Taking a snapshot > > So far so good. The filesystem size is 6MB and the snapshot 0MB > > Now I edit the first 4 characters of the text file. I would have expected the size of the snapshot to have grown by the size of the changed *blocks* but when I do a ''zfs list'' the filesystem is now reported as being around 12MB total with the snapshot around 6MB. > > So the snapshot is being reported as being the size of the changed *files* and not the changed *blocks*. Is this corret (that the snapshot is consuming this space) or is that just how it''s being reported with th zfs list command? > > Many thanks - Matt > > > This message posted from opensolaris.org > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss-- Eric Schrock, Fishworks http://blogs.sun.com/eschrock
On Wed, Jan 23, 2008 at 11:11:38AM -0800, Matt Newcombe wrote:> Creating an empty zpool & zfs > Creating a 6MB text file > Taking a snapshot > > So far so good. The filesystem size is 6MB and the snapshot 0MB > > Now I edit the first 4 characters of the text file. I would have > expected the size of the snapshot to have grown by the size of the > changed *blocks* but when I do a ''zfs list'' the filesystem is now > reported as being around 12MB total with the snapshot around 6MB.How did you edit the file? Are you sure that the editor didn''t just create a temporary file and rename it (thus updating every block)? -- Darren Dunham ddunham at taos.com Senior Technical Consultant TAOS http://www.taos.com/ Got some Dr Pepper? San Francisco, CA bay area < This line left intentionally blank to confuse you. >
OK, to answer my own question (with a little help from Eric!) ... I was using vi to edit the file which must be rewriting the entire file back out to disk - hence the larger than expected growth of the snapshot. Matt This message posted from opensolaris.org