We have always used software compression in the past because our tests
showed that software compression used less tape and cloning was faster.
We have not tested this with our new LTO-2 drives so I do not know if
this is still true.

We are currently in the process of adding a Windows Storage Node and
Windows Clients to our original configuration of a UNIX Server with only
UNIX clients.  

The LTO-2 tape drives on the Windows Storage Node have compression
turned on.  We are now running into problems and are considering
switching to hardware compression for our UNIX backups.

Our configuration is:

StorageTek SL500 library
Server - Solaris 10, Networker 7.2.1, 4 SCSI attached LTO-2 drives and 1
SDLT drive
Storage Node - Windows 2003, Networker 7.2.1, 2 SCSI attached LTO-2
drives

We were able to backup Windows clients but got the following errors when
we were trying to recover:

03/14/06 13:41:20 nsrd: media warning: rd=tor-prdbkp-s01:\\.\Tape0
moving: fsr 2
131: The semaphore timeout period has expired.
03/14/06 13:41:20 nsrd: media emergency: could not position 100059 to
file 105, 
record 14751
03/14/06 13:41:25 nsrd: media warning: rd=tor-prdbkp-s01:\\.\Tape0
reading: The 
I/O bus was reset.

We think that this might be because the indexes (which the Server wrote)
are also written onto the same tapes (same pool) from previous (test)
backups and the Server is not using compression but the Storage Node is.
So we have a mix of hardware compressed and non-hardware compressed data
on the same tape.

1) Are we on the right track with compression causing the problem?

2) What effect will turning on hardware compression on the drives
attached to the UNIX Server be?  (How much of a headache will it be to
switch after using software compression?  Note that our retention policy
is very long for some of our pools and we have been using LTO-2 tapes
for several months.  In fact we do not recycle our full backup pool
tapes)

3) Do we need to mark all previously partially written tapes as read
only or can we append to them?  

4) Can we still recover from tapes that were not written with hardware
compression on devices that now have hardware compression "enabled".

5) Which drives are used for cloning when you have a storage node
(drives only on the server)?  When we restricted the windows backup pool
and clone pool to the tape devices on the storage node cloning failed
(as well as writing the indexes).

Teresa Kroeker
Carswell

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