zfs: the exponential file system from hell

[Borja Marcos]

On Sep 27, 2013, at 2:29 PM, Attila Nagy wrote:

> Hi,
> 
> Did anyone try to fill a zpool with multiple zfs in it and graph the space accounted by df and zpool list?
> If not, here it is:
> https://picasaweb.google.com/104147045962330059540/FreeBSDZfsVsDf#5928271443977601554

There is a fundamental problem with "df" and ZFS. df is based on the assumption that each file system has 
a fixed maximum size (generally the size of the disk partition on which it resides).

ZFS is really different, though. Unless you assign them fixed sizes, it works much like a virtual memory system. There
is a large pool shared by all the datasets, and *any* of them can grow to the maximum pool size, that's the data
"df " shows.

With virtual storage allocation, compression and deduplication you can no longer make the old assumptions you made
in the old days. 

Anyway, in a system with variable datasets "df" is actually meaningless and you should rely on "zpool list", which gives you
the real size, allocated space, free space, etc.


% zpool list
NAME   SIZE  ALLOC   FREE    CAP  DEDUP  HEALTH  ALTROOT
pool  1.59T   500G  1.11T    30%  1.00x  ONLINE  -
% 

Times change, embracing the satanic filesystem implies that you have to change your mindset (and your scripts!)  :)








Borja.