ADSM-L

Re: [ADSM-L] Just how does a VTL work?

2007-06-15 17:26:59
Subject: Re: [ADSM-L] Just how does a VTL work?
From: Curtis Preston <cpreston AT GLASSHOUSE DOT COM>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Fri, 15 Jun 2007 17:26:00 -0400
It really is all over the board as to the details...  

Think of it as a custom filesystem with a really large block size.  (As
in 64 or 256 MB instead of the typical 8K you see in a normal
filesystem.)

As to how the whole deduplication thing works, you can read an article I
wrote on the subject here:

http://tinyurl.com/3588fb


---
W. Curtis Preston
Author of O'Reilly's Backup & Recovery and Using SANs and NAS
VP Data Protection
GlassHouse Technologies


-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Steven Harris
Sent: Monday, June 11, 2007 4:31 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] Just how does a VTL work?

Allen S. Rout wrote:
> This is irrational to some extent, I recognize.  But for the VTL, I
> don't know where the database is; it's _magic_.
>
> - Allen S. Rout
>
Good point Allen,

I realize that  VTLs come in different flavours from several
manufacturers, but is there any information about how their gizzards are
arranged?

I'd particularly like to understand how tape blocks are mapped to disk
blocks, and how the de-dup technology is organized.  There are a number
of possible implementations, and I can see that DB searches/updates
could become an enormous bottleneck particularly in a windows
environment with potentially thousands of identical copies of windows
system files.  This raises the spectre of another proprietary database
to be managed, grown, reorganized and re-indexed with limited
facilities.

Does anyone have pointers to this sort of information or is it a deep,
dark commercial secret?

Thanks

Steve

Steven Harris
AIX and TSM Administrator
Brisbane Australia

Moving to Sydney Mid July - Offer me a job now and avoid the rush!