[OpenAFS] Check free space on AFS share before login

Wed, 1 Feb 2017 12:29:53 -0500

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On 2/1/2017 5:08 AM, Richter, Michael wrote:
> Hi,
>=20
> we are using  OpenAFS for the home drive. /home/users is a symlink to
> the AFS path with all the home shares. The users home is for example
> /home/users/username.
>=20
> The users only have 1 GB of space available in that share. It often
> happens that the quota is reached and they are unable to login. Ubuntu
> doesn=E2=80=99t give a meaningful error message. I think, Ubuntu doesn=E2=
=80=99t know
> what=E2=80=99s the problem, because it sees only =E2=80=9C/=E2=80=9D as=
 mountpoint, which has
> enough free space available.

The OpenAFS Unix cache manager exposes AFS mount points as directories
not as symlinks and not as mount points.  From the perspective of
applications all of /afs is a single device consisting of every AFS
volume in the world.

In addition, while the file server offers the RXAFS_GetVolumeStatus RPC
which returns

 . the size of the partition
 . the amount of free space on the partition
 . the size of the volume quota (if any)
 . the remaining free volume quota (if any)

the OpenAFS Unix cache manager never queries it.  As a result, the
application only finds out that partition is full or the quota exceeded
during the close() system call.  If the quota is 2MB and an application
opens a file and writes 100MB and then closes the file without checking
the error code, the data is lost and the application believes the data
was written to the file server successfully.

As others have indicated, this is not how the Windows cache manager
works.  The Windows cache manager is aware of how much free space the
volume has and returns an error to the application as soon as the free
space reaches zero.  In addition, because the Windows cache manager
exposes each AFS volume as a separate device, it is possible to:

 . report some volumes as readonly and others as read/write
 . return accurate volume size and free space info for each path
 . report accurate quota information for each path
 . return out of space and out of quota errors on one path without
   causing the VFS to report those same errors on other paths

David Howell's kafs, the Linux in-tree AFS client, behaves in a manner
similar to the Windows client.

  https://www.infradead.org/~dhowells/kafs/

kafs requires testing, it requires that end user organizations inform
their preferred Linux distributions that building and distributing kafs
is important.  AuriStor, Inc. supports David Howells' development of
kafs.  Others should as well.

Jeffrey Altman

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n:Altman;Jeffrey
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email;internet:jaltman@auristor.com
title:Founder and CEO
tel;work:+1-212-769-9018
note;quoted-printable:LinkedIn: https://www.linkedin.com/in/jeffreyaltman=
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