Hi Marc
That's a very interesting topic for discussion and sharing!
An AFD (or FD (file type device), for that matter) is just a directory on a
file system on a disk. Given most 'standard' environments, that means that
this disk is dedicated to and connected to only one system (I'm ignoring
clusters right now). So, there is not the opportunity to create one big
data tub, and have all storage nodes pour their data into it. I really like
the consolidation possibilities that this could bring.
Tape devices (and virtual tape libraries, which emulate tape devices) can
and are shared among multiple systems in a storage area network. The
primary reason for this is that tape devices do not have a file system or
volume information that is tied to a particular operating system or host
system. So, you can just mount/write/dismount, connect this drive to the
next system (via the SAN), and mount/write/dismount again. The backup
software provides, if you will, the on-tape 'file system', and this can be
(and, in NetWorker's case, is) recognized by backup software running on
different operating systems.
But, there are good reasons for creating a small number of disk data tubs,
and having multiple systems write to them concurrently. What's needed is a
global/shared file system that runs over SANs, performs block I/O (not file
I/O like NAS, for performance reasons) and provides volume/file sharing.
While neither commonly discussed nor widely implemented for backup uses,
these file systems do exist. A good example is the ADIC StorNext File
System.* This allows the creation of, for example, a small number of very
large volumes that can receive backup-to-disk data streams simultaneously.
This product even supports multiple operating systems writing to the same
file system, something very few other products that I've examined can do.
This product arose out of the video broadcast industry's needs, I believe.
That's important because video generates long-running, high-I/O large block
data streams, which is just what backups generate; so, a good product from
the video broadcast world would perform well in 'our' world, methinks.
But, you ask, what about NAS? NAS devices already provide heterogeneous
sharing at the file system level. My own view is that this is nowhere near
as good a solution as a SAN-based solution, because it requires the
resource-intensive use of IP to carry the data from the storage node to the
NAS device.
If you have thoughts on this, have used products in this space, or know of
other products, please contribute to this discussion.
Many thanks!
tl
*Note that this is an observation, shared among this community of peers, and
not a recommendation by me nor my employer.
Terry Lemons
>CLARiiON Applications Integration Engineering
EMC²
where information lives
4400 Computer Drive, MS D239
Westboro MA 01580
Phone: 508 898 7312
Email: Lemons_Terry AT emc DOT com
-----Original Message-----
From: Marc Levitan [mailto:marc.levitan AT PFPC DOT COM]
Sent: Tuesday, September 16, 2003 2:50 PM
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Subject: Re: [Networker] Advanced File Device Size
Does anyone have the AFD working in a SAN?
Could you share your setup?
I was told that a "virtual tape library" would be needed to share the AFD
accross the SAN???
Thanks.
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