[OpenAFS] Re: volume size

[Andrew Deason]

On Fri, 14 Jan 2011 11:43:50 -0500
"Lewis, Dave" <LEWIS@NKI.RFMH.ORG> wrote:

> I'm wondering what is a reasonable size for large AFS volumes. I
> understand that the maximum size of a volume is about 2 TB (assuming
> that the partition is at least that size).

2T is the largest quota you can assign to a volume. If you don't give it
a quota, I think volumes can grow to larger than that. Some information
reported by tools will get a bit confused, but I don't think anything
would actually prevent you from accessing data on the volume.

> From a practical standpoint, is it reasonable to have a 2 TB volume?
> Should I expect any problems doing operations like bos salvage or vos
> move on large volumes?

They just take a lot longer. For moves that shouldn't matter as much,
since you can use a volume for most of the move, but salvaging will be
painful. And since we unfortunately don't display any kind of progress
during those operations, it can make it more difficult to tell if
something is hanging or just slow. ('vos status' can tell you a kind of
progress during moves, though)

> For example, I'm wondering if bos salvage has a "harder" time with a few
> large volumes than with several smaller volumes. I figure that, with
> smaller volumes, internal inconsistencies that bos salvage fixes would
> be more isolated than with large volumes, and that that would be
> beneficial. But I don't really know.

The difference in salvaging depends more on the number of files, not
necessarily the size of the volume. Salvaging will take more time,
consume more memory, and more temp disk space, which can be a problem
obviously if it uses up a significant portion of memory or disk space on
the server.

What may be more important is that if you can split the data into
smaller volumes, you can get a portion of the data online more quickly,
and it's easier to move the volumes around on different servers. That
is, if the user has 1 500G volume, you have to wait for the whole thing
to salvage; but if they have 5 100G volumes, you can get 1/5 of the data
available more quickly.

But the above refers to manual salvages or demand-salvages. If the
fileserver crashes and you salvage the whole partition, it doesn't much
matter.

-- 
Andrew Deason
adeason@sinenomine.net