Robert Thurlow wrote:
Harry Putnam wrote:
I think this has probably been discussed here.. but I'm getting
confused about how to determine actual disk usage of zfs filesystems.
Here is an example:
$ du -sb callisto
46744 callisto
$ du -sb callisto/.zfs/snapshot
86076 callisto/.zfs/snapshot
Two questions then.
I do need to add those two to get the actual disk usage right?
Is something wrong here... there are only 2 snapshots there.
And I've seen it mentioned repeatedly about how little space snapshots
take.
'du' does a stat() of each file it finds; it sees and reports
identical files in snapshots as full size. 'rsync' will also
work on all copies of a file.
To see space usage, you need to ask zfs itself:
NAMEUSED AVAIL REFER MOUNTPOINT
rpool/ROOT 10.4G 7.93G18K /rpool/ROOT
rpool/r...@rob 0 -18K -
The snapshot I just took and named after myself doesn't yet
take any space for itself. If I delete a file, e.g. my
/var/crash/* files that I'm done with, I *may* see space
start to be accounted to the snapshot.
Rob T
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As Robert pointed out, you DON'T want to use 'du', as it doesn't take in
account that ZFS use Copy On Write to reduce the amount of space that
snapshots take up. Think of it as similar to the situation you face
with hard links (i.e. multiple identical files actually all referring to
the same bits on the disk).
Remember, there are generally TWO concepts you don't want to confuse: a
FILESYSTEM, and a POOL. The Pool is the larger object, inside which
multiple filesystems, snapshots, and volumes can exit. A pool has a hard
limit as to the amount of space it can handle, as determined by the
underlying storage objects that make it up (disks, arrays, LUNs, etc).
The other objects are flexible size, up to the amount of the pool that
contains them.
By your question, you seem to be interested in the available/used space
of a Pool. You want the 'zpool' command for this, specifically:
zpool list
Look at the zpool(1M) man page.
To look at the size of FILESYSTEMS, you can use 'df' for a mounted
filesystem, as normal. Alternately, use 'zfs list filesystem' to list
a specific filesystem by name (i.e. data/foo/bar/baz ), or 'zpool list
-t type' where type is one of 'filesystem', 'snapshot', or 'volume'
to list all occurrances of that type of object.
Look at the zfs(1M) man page.
Note that most the output uses Human readable info, so it's going to
report GB and TB, not Bytes.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
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