Re: Understanding "btrfs filesystem usage"

[Ulli Horlacher <framstag@rus.uni-stuttgart.de>]

On Mon 2018-10-29 (17:57), Remi Gauvin wrote:
> On 2018-10-29 02:11 PM, Ulli Horlacher wrote:
> 
> > I want to know how many free space is left and have problems in
> > interpreting the output of: 
> > 
> > btrfs filesystem usage
> > btrfs filesystem df
> > btrfs filesystem show
> 
> In my not so humble opinion, the filesystem usage command has the
> easiest to understand output.  It' lays out all the pertinent information.
> 
> You can clearly see 825GiB is allocated, with 494GiB used, therefore,
> filesystem show is actually using the "Allocated" value as "Used".
> Allocated can be thought of "Reserved For".

And what is "Device unallocated"? Not reserved?


> As the output of the Usage command and df command clearly show, you have
> almost 400GiB space available.

This is the good part :-)


> The disparity between 498GiB used and 823Gib is pretty high.  This is
> probably the result of using an SSD with an older kernel.  If your
> kernel is not very recent, (sorry, I forget where this was fixed,
> somewhere around 4.14 or 4.15), then consider mounting with the nossd
> option.

I am running kernel 4.4 (it is a Ubuntu 16.04 system)
But /local is on a SSD. Should I really use nossd mount option?!



> You can improve this by running a balance.
> 
> Something like:
> btrfs balance start -dusage=55

I run balance via cron weekly (adapted 
https://software.opensuse.org/package/btrfsmaintenance)


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
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