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Re: [libvirt] directory storage pools reported available space



On Fri, Dec 03, 2010 at 12:00:39AM -0600, Ryan Harper wrote:
> We recently had an issue with not being able to allocate the full
> capacity of a directory based storage pool.  The reported value via
> pool-info was larger than what was available to the image creator.
> 
> Looking at the storage code, in virStorageBackendFileSystemRefresh()
> we're using statvfs, and reporting back 
> 
>    pool->def->available = ((unsigned long long)sb.f_bfree *
>                           (unsigned long long)sb.f_bsize);
> 
> Which is the amount of blocks available, including any root reservation
> if present on the filesystem.
> 
> This does't line up with df output , which at least on RHEL5 and 6
> systems reports the available space from f_bavail, which excludes
> and reserved space.
> 
> Is it reasonable to have the available value line up with output from df
> and not report reserved space?

I guess it depends on the usage scenario :-(  If you're allocating
a disk volume upfront with qemu://system, then reserved space is
irrelevant since libvirtd (which does the pre-allocation) is running
as root. If you are running qemu://session then we're non-root so
reserved space does matter.  With sparse files, reserved space does
matter if you want to calculate overcommit since QEMU runs non-root.
The problem is that I don't really see how to nicely fit this into
the storage pool model.

Daniel


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