Mark - thank you very much for your explanation and example. I really appreciate. Any ranting below is directed at ZFS, not you. =)
> > Snapshot Used Total (GB) == 766.73 > > Filesystem Referenced Total (GB) == 2570.04 Total of Snap Used + FS > > Ref (GB) == 3336.76 > > > > Vol0 filesystem Used (GB) == 5159.35 > > The sums don't really work that way. I followed your recipe, except using a 70MB tarfile instead of a 1GB file: > Consider this scenario: > - I create a dataset and copy 1g into it titan[root]:/> zfs create vol0/testfs titan[root]:/> zfs list vol0/testfs NAME USED AVAIL REFER MOUNTPOINT vol0/testfs 52.3K 1.58T 52.3K /vol0/testfs titan[root]:/> cd /vol0/testfs titan[root]:/vol0/testfs> tar cvf test.tar /groups/eng_staff titan[root]:/vol0/testfs> zfs list vol0/testfs NAME USED AVAIL REFER MOUNTPOINT vol0/testfs 72.4M 1.58T 72.4M /vol0/testfs > - I take a snapshot of it, @snap1 titan[root]:/vol0/testfs> zfs snapshot vol0/[EMAIL PROTECTED] titan[root]:/vol0/testfs> zfs list -r vol0/testfs NAME USED AVAIL REFER MOUNTPOINT vol0/testfs 72.4M 1.58T 72.4M /vol0/testfs vol0/[EMAIL PROTECTED] 0 - 72.4M - > - I copy 1g more data into the datset titan[root]:/vol0/testfs> tar cvf test2.tar /groups/eng_staff titan[root]:/vol0/testfs> zfs list -r vol0/testfs NAME USED AVAIL REFER MOUNTPOINT vol0/testfs 145M 1.58T 145M /vol0/testfs vol0/[EMAIL PROTECTED] 48.0K - 72.4M - titan[root]:/vol0/testfs> du -sh . 145M . > - I take another snapshot, @snap2 titan[root]:/vol0/testfs> zfs snapshot vol0/[EMAIL PROTECTED] titan[root]:/vol0/testfs> zfs list -r vol0/testfs NAME USED AVAIL REFER MOUNTPOINT vol0/testfs 145M 1.58T 145M /vol0/testfs vol0/[EMAIL PROTECTED] 48.0K - 72.4M - vol0/[EMAIL PROTECTED] 0 - 145M - > - I delete the two 1g files. titan[root]:/vol0/testfs> rm test.tar test2.tar titan[root]:/vol0/testfs> zfs list -r vol0/testfs NAME USED AVAIL REFER MOUNTPOINT vol0/testfs 145M 1.58T 145M /vol0/testfs vol0/[EMAIL PROTECTED] 48.0K - 72.4M - vol0/[EMAIL PROTECTED] 0 - 145M - After a minute: titan[root]:/vol0/testfs> zfs list -r vol0/testfs NAME USED AVAIL REFER MOUNTPOINT vol0/testfs 145M 1.58T 52.3K /vol0/testfs vol0/[EMAIL PROTECTED] 48.0K - 72.4M - vol0/[EMAIL PROTECTED] 72.4M - 145M - > What's left on the system? The first file is available via > both the snapshots, and the second file will be available via > the second snapshot only. In other words, @snap1 will have a > 'refer' value of 1g, and @snap2 will have a 'refer' value of > 2g. The dataset itself will only 'refer' to the overhead, > but will have a 'used' value of 2g. And you're completely correct! > However, the 'used' values of @snap1 and @snap2 will only > contain the deltas for the snapshots. @snap1 will contain > just the filesystem metadata for the 'used' - around 16-20k, > and @snap2 will contain the metadata plus the second 1g file. > > So, crunching the numbers using the method outlined above, > the snapshot used total is approx 1g, and the filesystem > refer total is 16-20k. These don't add up to the amount of > data still being consumed by the pool (the two 1g files), > because used & refer are tracking different pieces of information. Right, so I follow everything you have said here... but I guess I'm still at a loss. I think based on this, there really isn't a good way to know how much space is being consumed by snapshots? The only way I can think of based on this is to use "zfs list" or "zfs get" to get the "referenced" numbers, ONLY for filesystems (annoyingly, "zfs get" doesn't seem to have a -t flag). Then I have to add up all of the referenced numbers. Only THEN can I subtract that number from the "used" number for the entire volume to find out how much is being consumed by snapshots. Is there any other way? Then back to the issue at hand... which was the point of this whole exercise: How do I figure out how much disk space is being used by a given snapshot, or group of snapshots? This all of a sudden feels like a huge limitation of ZFS. I'm already dealing with the annoyance of not having quotas... now I feel more at sea without a rudder given that I can't even tell what disk space is being used by my snapshots! thanks johnS _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
