Stupid question regarding ZFS and `df -h` output

Matthew Seaman m.seaman at
Mon Apr 11 15:12:25 UTC 2016

On 2016/04/10 13:00, Aleksander Alekseev wrote:
> I installed FreeBSD using steps like "Next -> Next -> ZFS -> use entire
> disk and don't bother me with stupid questions -> Next"
> I have 128 Gb hard drive:
> ada0 at ahcich0 bus 0 scbus0 target 0 lun 0
> ada0: Serial Number 82GS10GGT2GY
> ada0: 600.000MB/s transfers (SATA 3.x, UDMA6, PIO 8192bytes)
> ada0: Command Queueing enabled
> ada0: 122104MB (250069680 512 byte sectors)
> And here is `df -h` output:
> Filesystem            Size    Used   Avail Capacity  Mounted on
> zroot/ROOT/default     95G     21G     74G    22%    /
> devfs                 1.0K    1.0K      0B   100%    /dev
> zroot/tmp              75G    153M     74G     0%    /tmp
> zroot/usr/home         89G     15G     74G    17%    /usr/home
> zroot/usr/ports        75G    859M     74G     1%    /usr/ports
> zroot/usr/src          76G    1.2G     74G     2%    /usr/src
> zroot/var/audit        74G     96K     74G     0%    /var/audit
> zroot/var/crash        75G    930M     74G     1%    /var/crash
> zroot/var/log          74G    360K     74G     0%    /var/log
> zroot/var/mail         74G    188K     74G     0%    /var/mail
> zroot/var/tmp          74G    136K     74G     0%    /var/tmp
> zroot                  74G     96K     74G     0%    /zroot
> How exactly should I read this to get result "all 128 GB are used"?

I take it you mean 'what would this output look like if all 128GB were
used'?   Because at the moment, you've got quite a lot of your disk
spaces still unused.

The 'Avail' column would show zero or a very small amount of space
available when the pool was full, and the figures for the 'Size' and
'Used' columns would have pretty near equal values.

The 'Size' and 'Capacity' columns are a bit weird in ZFS -- unlike a
system with fixed size filesystems where the meaning of those columns is
clear, with ZFS  'Size' means "The sum of the already used space for
this ZFS plus all of the available space in the entire pool"[*] -- so
'Size' for one ZFS will change as data is added to another ZFS.
Capacity is just the ratio of 'Used' over 'Size', and shows similar effects.



[*] Assuming that there haven't been any reservations or size limits
configured for that ZFS, which is generally the case for what the
installer creates.

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