I am not quite sure what you meant by "with TSM you can use disk only
for backups instead of onsite tape".  I do not see any reason why you
can not use FILE device types for both primary and copypool stg pools.
Of course if you actually want to move a copy of the data offsite, then
you would need some type of removable media such as tape.

For me two of the attractions of a virtual tape library are being able
to do lanfree backups without using Sanergy, and having the VTL do
compression. 


H. Milton Johnson

 
-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Prather, Wanda
Sent: Tuesday, September 28, 2004 2:57 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: direct attached disk (DAS) at a tape library?

If you read the thread "D2D on AIX" over the past week, it has lots of
details on the pros and cons of using Disk only for backup.  The answer
overall, is that with TSM you can use disk only for backups instead of
onsite tape, as long as you do a little advance planning.  I think the
virtual tape libraries may be more attractive to sites with non-TSM
applications that are written specifically for tape.

My concern is your statement that "we don't remove tapes anyway".

What do you do if 1) you lose your disk array, or 2) someone sets your
building on fire?

One of the advantages of tape, is that you can make as many extra tapes
as you want, and send them somewhere in case of a building disaster.

You can also keep adding storage space 200GB (one cartridge) at a time,
without making an additional capital purchase.

Still, a lot of people, and maybe you, will find that for at least the
primary copy, disk-only is very cost effective as a backup pool.

But,
BE VERY CAREFUL about the quality of disk you buy, if that is going to
be your only copy of the data.
DO NOT THINK that you can't lose a RAID array; I have seen it happen,
twice.
It depends TOTALLY on the quality of the controller card in the RAID
array.
If it goes south, all you've got is a bunch of unrelated magnetized bits
on your disk.

And for sites that have ARCHIVE or HSM data (which may not exist any
more on the client machines), there is NO magnetic media reliable enough
that you can be safe with just 1 copy (except maybe those tapes they put
in airline black-boxes, but I don't know where to buy those :>).

Wanda Prather
"I/O, I/O, It's all about I/O"  -(me)






-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Alexander Lazarevich
Sent: Friday, September 24, 2004 6:17 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: direct attached disk (DAS) at a tape library?


We have TSM 5.1.6.5 on win2k server. library is overland neo 4100 (60
tape capacity) with 2 X HP LTO-2 drives. We need another 12TB of backup
capacity. We are considering getting something other that another tape
library.

Couldn't we buy a couple of 6.4TB SCSI-SATA RAID DAS devices, and attach
that to our backup host via SCSI, and start using that DAS as one big
disk(tape)? We would just tell TSM that the big disk is some massive
spool, or even a tape. We could even buy several of the DAS units, and
just keep adding them as spool (or tape) disks on the SCSI chain. This
would give us FAST backup and restore.

Why do we need tapes? I know there are disk systems like the Reo, which
is just a DAS RAID that does tape virtualization, but those things cost
3 times as much as a regular DAS. Why is tape virtualization so
expensive?
Why do we need tape virtualization?

Is there something about how TSM handles disks vs. tapes, that makes
using DAS impossible, or not a good idea?

We are not too worried about reliability. We think we can configure
multiple RAID arrays on the devices so that we lessen the chance of disk
failure causing backup data loss.

There must be some things we don't realize that tape virtualization
gives us that a bunch of DAS disks won't. Price isn't it though, because
we can get 13TB of DAS for 24K. The equivalent in LTO-2 tape (with
library) costs 35K. And Disk to Disk backup is even more, like 44K!

The only disadvantage we can come up with are that we can't remove
tapes.
But we don't remove tapes anyway.

Please tell me why we shouldn't just attach a big 13TB DAS to our TSM
host, and start using that as the main backup disk.

Thanks,

Alex
---                                                               ---
    Alex Lazarevich | Systems Administrator | Imaging Technology Group
     Beckman Institute | University of Illinois | www.itg.uiuc.edu
---                                                               ---