Does your application depend on, or report, free disk space? Re: F20 Self Contained Change: OS Installer Support for LVM Thin Provisioning

[Lennart Poettering]

On Fri, 26.07.13 21:29, Eric Sandeen (sandeen at redhat.com) wrote:

> On 7/26/13 3:13 PM, Miloslav Trmač wrote:
> > Hello all,
> > with thin provisioning available, the total and free space values
> > reported by a filesystem do not necessarily mean that that much space
> > is _actually_ available (the actual backing storage may be smaller, or
> > shared with other filesystems).
> > 
> > If your package reports disk space usage to users, and bases this on
> > filesystem free space, please consider whether it might need to take
> > LVM thin provisioning into account.
> 
> Short answer: it doesn't (it can't).
> 
> Just like an application doesn't know if it's got a 2.5" or 3.5" drive
> behind it, or cloud behind it, or a usb stick behind it, it doesn't
> know if it's got thinly provisioned storage behind it.

Well, correct me if I am wrong but don't RAID devices communicate
certain metrics to the file systems on them already? (stride size
iirc?). It doesn't sound too difficult to communicate the thin
provisioning ratio as well, and then leave it to the file system to
scale the report disk free space.

> > The same applies if your package automatically allocates a certain
> > proportion of the total or available space.
> 
> I can't imagine that anything actually does that, does it?
> Good lord I hope not.  ;)

journald does that (see other mail).

Lennart

-- 
Lennart Poettering - Red Hat, Inc.