> Question : I gather Deduplication is using other software. 
> DataDomain i
> think i saw mentioned. Where does this fit in with Netbackup and does
> the software reside on every client or just a server somewhere?

In the technologies I'm familiar with--one of them is old, another new,
it's conceptually simple.  "The system," whether that's a standalone
system or a box of disk with some smarts or an agent on the backup
client, receives data and examines it in blocks of some size (AFAIK,
always way larger than a 512-byte disk block).  Simplistically, it
checksums the "block" and looks in a table of
checksums-of-"blocks"-that-it-already-stores to see if the identical
<ahem, anyone see a hole here?> data already lives there.  If so, the
data can be tossed away and the checksum kept.  The "file" as stored as
a collection of these checksums (imprecise term, but works for the
example) or a list of pointers to the single instance (hence the SIS
term can be overloaded here) of the data represented by that checksum.
A simplistic example would be storing a TB of zeros.  Deduplicating
devices would store the first "block" of zeros, then find that all the
rest of them were the same checksum, same data and just store one more
pointer.  That 1TB file becomes, say, one real instance of 512KB of
zeros (if that is the "block" size) plus the space for a few million
pointers to the same 512KB of data.  Obviously, even this could be
compressed but that's another story.

Backing up the same system with few changes would be a very small full
backup.  Backing up many instances of, say, the C drive of w2k3 systems
will deduplicate like crazy.  Backing up a million different JPEGs
wouldn't save any appreciable space, but backing them up twice, or
multiple instances of the same JPEG, would.

> LTO3 tapes are storing 200gb a tape which is pretty good compared to
> disk i thought.

But that's a horrible number for LTO3.  Either your tapes aren't full or
something is broken.  Look at the available_media report to get a good
idea of the range of data stored on your FULL tapes.


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