Tell me if I'm wrong but my understanding of tape compression is:

Let's say I have a 50GB chunk of data available on a very fast
disk/SCSI/PCI/etc.
and let's say I can backup that 50GB chunk of data in 1 hour.

Assume I'm using a DLT8000 tape drive which has a native streaming speed of
6MB/s assuming no compression and a DLTIV tape in a DLT8000 drive with no
compression on the data will fit 40GB of data on that tape.

So that means my avg throughput is 50000MB/(1*60*60)sec or 13.88MB/s
And my compression ratio is 13.88/6  or 2.31:1

And also during the backup on the average I will see the throughput
indicated by the NetWorker Admin GUI as 13.88
And furthermore I'm fitting 50GB of data(compressed) onto a tape that only
holds 40GB in native(no compression)mode.

Bottom line is that NetWorker has no idea that the tapedrive is compressing
the data other than the fact that it's able to write data to it at an
apparent rate faster than the native write rate for the DLT8000 of 6MB/s.

Could a typical case of something like this happening be an Exchange
Database of size 50GB where most users have been deleted but no defrag has
been done yet - the apparent backup throughput could be apparently very fast
to do the 50GB because large chunks of it are very compressible.
And then after the Db is defragged and the Db size dropped from 50GB to 10GB
the backup time being just as long or longer because there's very little
compression and the apparent throughput displayed by NetWorker is
considerably slower.

If you don't believe this, then please tell me where I'm going wrong...

thanks - John


-----Original Message-----
From: Zaigui Wang [mailto:zaigui AT YAHOO DOT COM]
Sent: Tuesday, November 26, 2002 10:10 AM
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Subject: Re: [Networker] Unit Attention Bus Reset


I've seen this error on EMC devices, which was fixed
with an EMC patch. Are you using any EMC storage by
any chance?

--- Greg Nicholson <gnicholson AT ENVISIONEMI DOT COM> wrote:
> During my morning rounds I was treated to this
> little nugget:
>
> "Server sparrow: SJI failure [0x  27]:Unit Attention
> Bus reset"
>
> I am running NetWorker 6.2 for Windows running on a
> Windows 2000 Server
> Jukebox is a Scalar 100 AIT3
>
> After checking "savegrp.log" it appears all
> groups/clients ran successfully
> (no unsuccessful saves appear).
>
> What could this message indicate?  Thank you for
> your help!
>
> Greg Nicholson
> Envision EMI, Inc.
>
> --
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