On 28 Sep 99, at 12:56, Remeta, Mark wrote:
> I would say if your tape drive has hardware compression, then don't
compress
> on the clients.
> If you must compress on the clients turn off hardware compression
on the
> tape drive. It really slows things down when the tape drive tries to
> compress data that is already compressed.
>
>

Like most things, nothing is simple . . . . .

We don't use ADSM currently, but were looking at it to replace our
current system.  In relation to compression I've got 2 issues to deal
with:

1) Our big systems have a mix of normal filesysems, and filesystems
containing already compressed data (via unix compress utility).

2) We backup a bunch of remote systems (T1 connected).  With our
current backup sftw, the only way I've found to keep backups from
completely dominating the comm circuits is to use client compression.
I trade off cpu cycles for less network bandwidth.

So I have a mix of local clients with a lot of already compressed
data and client compressed data from remote systems, all comming into
the same backup sftw/jukebox/tapedrives.  My solution, since I have a
majority of local systems with normal uncompressed data, is to have
the tape drives set to compress - knowing full well that I'm probably
increasing the actual backup size.  I use AIT1 drives.  When backing
up the already compressed data I  get throughput of about 2.8mBps -
very close to the drives 3mBps rating.

From what I've seen with ADSM, I'd have to set it up the same way.

While I'm sitting here writing this email, I've been thinking that I
read something somewhere about a tape drive that could dynamically
determine if the data it was handling was compressable.  If the data
stream wasn't compressable it would quit trying to compress it - all
on the fly.  Does this ring a bell with anyone else????

Rick



----------------------------------------------------------------------
Richard L. Rhodes     e: rhodesr AT firstenergycorp DOT com
Richard L. Rhodes     e: rhodesr AT firstenergycorp DOT com
Ohio Edison Co.       p: 330-384-4904
                      f: 330-384-2514