Understanding ZFS Snapshots - why will it utilize space ? Post: 303013387

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Operating Systems Solaris Understanding ZFS Snapshots - why will it utilize space ? Post 303013387 by Peasant on Tuesday 20th of February 2018 03:34:50 PM

02-20-2018

Moderator

After the deletion of file1 USEDSNAP is telling you that there are pointers to 100MB of data.
In that time, 2 references exist in point in time for 100M of data.
snap1 - file1
snap2 - file1, file2

USED space in zpool has not changed after the deletion of file1.

Now, tank@snap1 is destroyed.
zfs list is telling you if you destroy the renaming snapshot (snap2), you will reclaim 100M of space as free space.
Since snap2 contains both files (one being 'live' one, other being referenced to) it is using 100M of space in zpool.

During the practice on the blog USEDSNAP column will always be 100M, after first snapshot creation, deletion of file1, second snapshot creation, first snapshot destroy.
This is not displayed clearly on the blog entry.

A good tehnical read Is it magic? | Oracle Matthew Ahrens' Blog

Hope that helps
Regards
Peasant.

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lzcmp

XZDIFF(1)							     XZ Utils								 XZDIFF(1)

NAME

       xzcmp, xzdiff, lzcmp, lzdiff - compare compressed files

SYNOPSIS

       xzcmp [cmp_options] file1 [file2]
       xzdiff [diff_options] file1 [file2]
       lzcmp [cmp_options] file1 [file2]
       lzdiff [diff_options] file1 [file2]

DESCRIPTION

       xzcmp  and  xdiff invoke cmp(1) or diff(1) on files compressed with xz(1), lzma(1), gzip(1), or bzip2(1).  All options specified are passed
       directly to cmp or diff.  If only one file is specified, then the files compared are file1 (which must have a suffix of	a  supported  com-
       pression  format)  and  file1 from which the compression format suffix has been stripped.  If two files are specified, then they are uncom-
       pressed if necessary and fed to cmp(1) or diff(1).  The exit status from cmp or diff is preserved.

       The names lzcmp and lzdiff are provided for backward compatibility with LZMA Utils.

SEE ALSO

       cmp(1), diff(1), xz(1), gzip(1), bzip2(1), zdiff(1)

BUGS

       Messages from the cmp(1) or diff(1) programs refer to temporary filenames instead of those specified.

Tukaani 							    2009-07-05								 XZDIFF(1)