2) Sepaton does hardware compression so as far as I can tell it performs like compression on physical drives, I imagine other vendors may also use hardware compression. Besides what's important to me is that my TSM clients and TSM server are not taking a performance hit from doing compression because compression has been off loaded to the VTL. Even if the VTL performs slower when compressing vs not compressing, it's not an issue unless your TSM server can over whelm your VTL. Any time your TSM server or TSM client is doing compression, your backup session performance is impacted.
3) This is an area that merits actual testing which is one reason I expressed it as a personal opinion. This seems to me that the results would be very dependent upon the exact hardware configuration being tested. At the least, using a VTL would off-load the file system management activities from the TSM server to the VTL freeing up TSM CPU cycles to pump data from the input stream to the output stream. 4) Read the article by Curtis Preston (referenced in the "Just how does a VTL work?" thread) for a discussion on in-band versus out-of band de-dup and the effect on performance. I agree this technology does not have a long track record and due diligence in progressing on this, and other new backup technologies, is strongly advised. As I stated I have not used this as of "yet". 5) If your VTL must run FSCK against 100TB, yes you do have a problem but: 5A) At least your TSM server is up. 5B) Your TSM server is a much more complex system compared to a VTL. Hence is most likely more susceptible to crashing. Thanks, H. Milton Johnson -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED] On Behalf Of Josef Weingand Sent: Sunday, June 17, 2007 2:58 PM To: [email protected] Subject: Re: [ADSM-L] Fw: How to Incorporate a CDL into TSM environment? 1.) yes 2.) pls give me vendor / machine type of VTLs which does compression without performance impacts. physical tape drives gets performance improvements of compression, but VTL gets normally much slower performance if compression is enabled 3.) you need compare the same technology. You need compare a FC Disk Subsystems, like DS4000, with a VTL, then you get the same performance (maybe even more) from a File Device Type as from a VTL. 4.)current de-dups does not bring enough performance for most of the environments, and in addition, most vendors have just announced it, but does not have it ready for GA yet. 5.)what happens if the VTL crashed???? Mit freundlichen Grüßen / Kind regards Josef Weingand Senior IT Specialist Technical Sales Systems Storage Mobil +49 171 55 26 783 - Homeoffice Tel. +49 8845 757421 Fax +49 171 13 5526783 email: [EMAIL PROTECTED] SMS/eMail: [EMAIL PROTECTED] IBM Deutschland GmbH Vorsitzender des Aufsichtsrats: Hans Ulrich Maerki Geschäftsführung: Martin Jetter (Vorsitzender), Rudolf Bauer, Christian Diedrich, Christoph Grandpierre, Matthias Hartmann, Thomas Fell, Michael Diemer Sitz der Gesellschaft: Stuttgart Registergericht: Amtsgericht Stuttgart, HRB 14562 WEEE-Reg.-Nr. DE 99369940 "Johnson, Milton" <[EMAIL PROTECTED]> Sent by: "ADSM: Dist Stor Manager" <[email protected]> 15.06.2007 21:08 Please respond to "ADSM: Dist Stor Manager" <[email protected]> To [email protected] cc 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: [email protected] 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
