I agree with Paul on this issue.

The same is true with the VTL that I currently use.

Kevin Whittaker 

-----Original Message-----
From: veritas-bu-bounces AT mailman.eng.auburn DOT edu 
[mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of Paul 
Keating
Sent: Monday, September 24, 2007 9:34 AM
To: Curtis Preston; Clem Kruger; VERITAS-BU AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] Script to label expired tapes in a VTL

Not entirely true, Curtis.

When your virutal tape expires, the VTL has no way of knowing this untill the 
tape is written to again.
Depending on the VTL, this may be too late.

I've got about 2TB of "free" space on my VTL, and about 1000 scratch VTs (2800 
total).

After a couple of weeks of Netbackup using and expiring VTs, The VTs are going 
back to Scratch, but untill they're re-written, the pointers in the repository 
still exist, therefore the VTL thinks the space is still in use....so if you're 
using a de-duping VTL (or DSU to a de-duping FS) and you're only doing "real 
time" freeing of space  (ie, re-labelling a VT only when you re-write it, or 
letting NBU delete images from the DSU only as the DSU approaches a high disk 
utilization threshold), then your target will need to do some high-perf 
defragging in order to provide you with sufficient "free" space to write more 
images.

Non-de-dup TLs such as Quantums, which "hard" allocate a fixed chunk of disk 
for each cart will not have this problem, nor will a DSU on a standard FS, but 
with my current VTL, it's definitely a requirement to occasionally kick off a 
script to "bplabel" recently expired tapes, so that the defrag process can run 
at a higher priority (when IO to the TL is lower.)

Paul

-- 


> -----Original Message-----
> From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
> [mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of Curtis 
> Preston
> Sent: September 22, 2007 5:15 AM
> To: Clem Kruger; VERITAS-BU AT mailman.eng.auburn DOT edu
> Subject: Re: [Veritas-bu] Script to label expired tapes in a VTL
> 
> Oversubscription aside, once his tapes are expired, the space taken up 
> by those tapes is immediately available for reuse.  The next time the 
> tape gets written to, it will delete all pointers to the space taken 
> up by that tape.
> 
> As to the VTL vs disk debate, I still think you should bring in all 
> disk devices and let them duke it out before excluding an entire 
> category of them.  You're going to exclude a lot of really good 
> products if you just "no VTLs."
> 
> Remember that saying "I don't want a VTL but I do want de-dupe" means 
> that you're going to use NAS.  While that will meet a whole lot of 
> needs for a whole lot of people, there's also some really big backups 
> that need a lot more than you can push over IP.  For those backups, 
> you're going to want a block transfer protocol (i.e. SCSI), and for 
> that, you're currently going to be buying a VTL.  (Unless you're just 
> going to buy a non-deduped disk in which case I'd say you're REALLY 
> wasting your
> money.)
> 
> ---
> W. Curtis Preston
> Backup Blog @ www.backupcentral.com
> VP Data Protection, GlassHouse Technologies -----Original Message-----
> From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
> [mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of Clem 
> Kruger
> Sent: Saturday, September 22, 2007 4:24 AM
> To: VERITAS-BU AT mailman.eng.auburn DOT edu
> Subject: Re: [Veritas-bu] Script to label expired tapes in a VTL
> 
> Hi Steve,
> 
> This is the downer on VTL's. You do not get your "tape" space back 
> automatically. It is for these reasons I recommend that one never go 
> VTL's. NetBackup 6.0 and 6.5 allow disk to disk backups; the images 
> are easily replicated to an offsite facility.
> 
> The time for all "tape" has come and gone. The de-duplication facility 
> in 6.5 makes life even easier. Why VTL's (which does SCSI emulation) 
> when you and use disk which is faster and has more protection?
> 
> Clem.
> 
> -----Original Message-----
> From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
> [mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of 
> swaltner
> Sent: 21 September 2007 17:32 PM
> To: VERITAS-BU AT mailman.eng.auburn DOT edu
> Subject: [Veritas-bu] Script to label expired tapes in a VTL
> 
> 
> We deployed a VTL last month, which has been working very nicely. This 
> is in a NetBackup 5.1 environment with the VTL attached to our Solaris 
> based master server as well as to our NAS server for local NDMP 
> backups.
> One thing I'd like to do is over-subscribe on the back-end storage, 
> but before I do that I'd like to automate the process of freeing up 
> the disk space used in the VTL when a NetBackup tape is expired. Just 
> curious if anyone has already written such a beast and would like to 
> share with me as a starting point.
> 
> If not, I suspect I'll use the following logic:
> 
> - Every day (at noon??), query the robots defined in the VTL and keep 
> a record of tapes that are allocated.
> - When a tape goes from allocated to non-allocated from one day to the 
> next, use a command like the following to erase the tape's contents:
> bplabel -erase -o -d dlt -m VTL123
> 
> This would write a small label at the beginning of the virtual tape, 
> causing the VTL to drop all the other data that had been stored on the 
> tape.
> 
> Any reason this wouldn't work? Any gotchas with writing this script 
> that I should look out for?
> 
> Steve
> 
> +-------------------------------------------------------------
> ---------
> |This was sent by steve.waltner AT lsi DOT com via Backup Central.
> |Forward SPAM to abuse AT backupcentral DOT com.
> +-------------------------------------------------------------
> ---------
> 
> 
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La version française suit le texte anglais.

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