EMC also has a tape emulator that goes in front of their ATA storage.  We
couldn't see any benefit to having tape emulation for TSM storage so opted
to just use the ATA storage.
Jim Sporer


At 10:41 AM 9/27/2004 -0500, you wrote:

Overland's Reo series is a DAS wrapped inside a virtual tape emulator.
That costs 3 times as much as the equivalent capacity of DAS. An Overland
Tech rep told me the only difference between a DAS and the Reo is the tape
emulation, and I have no idea why it costs that much. LTO-2 tape is about
2.5 times as much as DAS.

Since we don't do offsite tapes, I'm wondering if we even need tapes or
tape emulation, and can just buy DAS and treat it as spool (tape), just
like you say JC. Does anyone else have any comment? Would love to get
more feedback.

Thanks!

Alex

On Fri, 24 Sep 2004, Coats, Jack wrote:

Yep, you can do it.

Overland also sells a virtual tape library, but I don't know about their
prices, and so do other vendors.  It is basically a bunch of disk, but looks
like tapes.

Why is virtual tape so expensive?  Well, IMHO ;) if folks will buy it at
that price, then they will sell it!!!  TSM doesn't have to have it, but
there may be some reasons why it is good.  I am sure someone can straighten
me out on it!

But you can set up a JBOD of any size with a file system on it.  You can use
it as a disk pool, or, if you are having some tapes still, you might take
some of it and define some serial storage on disk.  It will process just
like tapes, just a lot faster.  Keeping your disk and on-site 'tape' pool on
disk devices is just fine, if you like its reliability!

To get stuff off site, I like keeping tapes.  $/gig, tapes are pretty cheap
and pretty reliable.

If you have the tape bandwidth, I would like an on-site copypool and an
offsite copypool on tape.  But that may just be my belt and suspenders
conservatism.

... Enjoy, JC

-----Original Message-----
From: Alexander Lazarevich [mailto:alazarev AT ITG.UIUC DOT EDU]
Sent: Friday, September 24, 2004 5:17 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
---                                                               ---