[OpenAFS-devel] Re: Backups using commercial products

[Lyle Seaman]

Mitch Collinsworth wrote:

> On Tue, 2 Jan 2001, Neulinger, Nathan R. wrote:
>
> > What I wonder is - how hard would it be to access the contents of an AFS
> > volume from a file server, without going through AFS itself - i.e. by direct
> > file access - sortof a really fast 'vos dump' equivalent.
>
> Good question.  Now that we have the source I'm sure it would be
> possible to figure out the structure and read it directly from
> disk.  Maybe somebody's even done this already.
>
> The other path to consider is that now that we have the source
> maybe someone will figure out why vos dump is so slow and fix
> it.

1. be sure to coordinate the volume access with the vol server so
that it doesn't get moved or deleted out from under you.  This is
trickier than it sounds.

2. vos dump is slow because
   i. it does a zillion seeks on the disk, one at a time.
   ii. it uses RX at the same time.

If you want to make it faster, you either have to use a different
local filesystem which keeps data and inodes closer together,
or you have to queue up all the disk I/O all at once, so the
disk scheduler can work more efficiently.  But then you may be
hurting fileserver latency.