[OpenAFS] Re: vos shadow to backup user homes

Jeffrey Hutzelman jhutz@cmu.edu
Mon, 26 Aug 2013 14:24:32 -0400

On Mon, 2013-08-26 at 10:28 -0500, Andrew Deason wrote:
> On Sun, 25 Aug 2013 21:05:41 +0530 (IST)
> Shouri Chatterjee <shouri@ee.iitd.ac.in> wrote:
> > I wanted to ask about "vos shadow" and whether it is being used as a
> > solution on production systems to back-up user home directories.
> I believe it is, but I'll let others speak if they are doing so.

I'll point out at this point that vos includes both high- and low-level
operations in one command-line tool, and sometimes it is hard to tell
the difference.  The high-level operations are things like create, move,
backup, release, and remove, which are intended to be used for everyday

Low-level operations like changeloc, clone, delentry, shadow, and zap
are intended for unusual situations or as building blocks for use in
more complex operations.

"vos shadow" by itself was not intended as a backup mechanism of any
kind.  Rather, it was intended to be used in constructing a system that
would create and track entire shadow servers, which could be easily
brought online if a "real" server failed.  I never built that larger
system, but perhaps others have done so.

> Yes, one of the downsides of shadow volumes is that using them is not
> documented as well as other features, and they aren't tested as much. 

Because there actually is no such feature as a "shadow volume".  Manual
pages notwithstanding, the "vos shadow" command does not "create a
shadow volume"; it merely provides a way to do the same sequence of
cloning and forwarding full and incremental dumps that is used by the
move and copy commands, but without deleting the source volume or making
any changes to the VLDB.

-- Jeff