I think you hit every nail right on the head, Milton. I would emphasize #5, as people tend to minimize how big of a deal it is to provision and administer large amounts of disk. A GOOD VTL (not all are good) will make that provisioning issue go away.
As to de-dupe, it's considered by many to be the hottest technology right now, and it is real, and is saving lots of people lots of money. It actually (in most cases) makes a VTL roughly equivalent (if not cheaper) than a similarly-sized tape solution. --- W. Curtis Preston -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED] On Behalf Of Johnson, Milton Sent: Friday, June 15, 2007 12:09 PM To: ADSM-L@VM.MARIST.EDU Subject: Re: [ADSM-L] Fw: How to Incorporate a CDL into TSM environment? Why a VTL vs FILE devclass volumes on local drives? 1) With a VTL you can do LAN free backups. 2) Data Compression: 2A) TSM Client does compression: Big performance hit on the client, slower backups/restores 2B) TSM server does compression (FILE devclass volumes on compressed file systems): Big performance hit on server, slower backups/reclaims/restores 2C) VTL does compression: No performance hits (just as with using physical drives with compression) 3) I doubt the TSM server could write large amounts of data simultaneously streaming in from 30 different clients to 30 different FILE devclasses volumes as fast as it can write that data to a fibre channel adapter. 3A) 30 input streams means 30 mounted FILE devclass volumes 3B) The drive heads would always be out of position for the next write. 4) Data Reduction/Data Deduplication/Content Aware Compression: What ever the VTL vendor calls it, you don't have that available with FILE devclass volumes. (I realize that from previous posts you are not comfortable with this technology, I myself have not used it.) 5) Do you really want to manage an AIX system with a 25TB, 50TB or a 100TB file system? After a system crash how long will a FSCK of 100Tb take? Thanks, H. Milton Johnson -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED] On Behalf Of Allen S. Rout Sent: Thursday, June 14, 2007 3:22 PM To: ADSM-L@VM.MARIST.EDU Subject: Re: [ADSM-L] Fw: How to Incorporate a CDL into TSM environment? >> On Wed, 13 Jun 2007 08:43:43 -0400, "Johnson, Milton" <[EMAIL PROTECTED]> said: > The VTL is a Sepaton S2100-ES and yes it is disk only. > I don't see the benefit that a "tape backed" system would bring, how > does that really differ from a physical tape ATL with TSM providing a > DISKPOOL front end? Well, exactly. :) But the distinction I wanted to make clear was: if you've decided to store all your data on disk, then TSM has all the primitives necessary to make that disk manageable, and you can discard the intermediate appliance that makes the disk pretend to be a bunch of tape drives. That's what everyone's getting at when they talk about FILE devclasses. So if you bought 23 TB of slow disk plus a pretend-im-tape-box, then the tape box was a waste, if you're using TSM. If you're using something without TSM's volume primitives, it could be extremely important. - Allen S. Rout