Looks like this was an oops on my part - I got it pointed out for me
that piping from /dev/zero to a filehandle results in a sparse file,
which I did not understand and which explains the lack of impact from
*that*.
I verified that compressratio reports properly when dumping highly
compressible ASCII into a dataset, so, false alarm - sorry 'bout that;
closing.
** Changed in: zfs-linux (Ubuntu)
Status: New => Invalid
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https://bugs.launchpad.net/bugs/1639963
Title:
zfs get compressratio returns bogus results
Status in zfs-linux package in Ubuntu:
Invalid
Bug description:
I'm running a just-installed-today copy of 16.04.1, installed from an
ISO also just downloaded today from releases.ubuntu.com.
root@xenial:~# lsb_release -rd
Description: Ubuntu 16.04.1 LTS
Release: 16.04
root@xenial:~# apt-cache policy zfsutils-linux
zfsutils-linux:
Installed: 0.6.5.6-0ubuntu14
Candidate: 0.6.5.6-0ubuntu14
Version table:
*** 0.6.5.6-0ubuntu14 500
500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64
Packages
100 /var/lib/dpkg/status
0.6.5.6-0ubuntu8 500
500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
I noticed that zfs get compressratio was not returning good results,
and tested to ensure it was the compressratio reporting that was
broken, not the actual compression. Demonstration:
root@xenial:~# zfs get compress data/test
NAME PROPERTY VALUE SOURCE
data/test compression gzip local
root@xenial:~# zfs list data/test
NAME USED AVAIL REFER MOUNTPOINT
data/test 2.64G 855G 2.64G /data/test
Note that data/test has inline gzip compression on, and shows 2.64G of
data USED.
root@xenial:~# du -hs --apparent-size /data/test
9.2G /data/test
root@xenial:~# du -hs /data/test
2.7G /data/test
Now note that du correctly shows us that we have 9.2G of data stored
in data/test (about 7G of which is actually a dump from /bin/zero for
max compressibility, the other bit being an Ubuntu VM image file).
We should be seeing a compressratio of about 3.41x.
root@xenial:~# zfs get compressratio data/test
NAME PROPERTY VALUE SOURCE
data/test compressratio 1.01x -
But we're seeing 1.01x. Obviously very much not correct.
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