It highly depends on what you are trying to achieve - cost, performance,
redundancy or mixture of them.
1. Cost - two hubs and single-attached drives split between them is the
cheapest (and worst in terms of performance/redundancy) solution.
2. Performance - do it all switched! Consider carefully not only
host-to-switch and switch-to-tape throughput but also potential
switch-to-switch bottlenecks (possibly non-TSM traffic). Special attention
should be paid on paths order/usage if redundant paths are available.
3. Redundancy - put a *pair* of switches and connect each drive to both!
You said plans are for upgrade to LTO-2. IBM Ultrium2 drives have two
ports and new Atape versions support SAN path failover.

Some of the comments were that you should have no more than 2 drives per
HBA. If you indeed achieve 5:1 compression this might mean even 2 will not
work at the maximum performance. OTOH if you have (or plan) SAN clients to
utilize extra drives the equation might be different - 2 HBAs x 2 drives +
2 drives for StA = 6. And then you should plan carefully not only TSM
Server-SAN-library route but also TSM StA-SAN-library one.

Zlatko Krastev
IT Consultant






Tom Kauffman <KauffmanT AT NIBCO DOT COM>
Sent by: "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>
10.09.2003 19:39
Please respond to "ADSM: Dist Stor Manager"


        To:     ADSM-L AT VM.MARIST DOT EDU
        cc:
        Subject:        How have you got your fiber-attached LTO drives 
connected to your TSM
server?


I will be going fiber-attach next year and will have two adapters in my
TSM
server.

Do I put a fiber switch in the tape library (3584), tie all the drives to
it, and run two fibers back to the TSM server?

Do I run seperate fibers for all the drives back to my existing switches?

Do I put a pair of fiber hubs in somewhere, and hook half the drives to
each
hub?

Ah, yes, it's that wonderful time of year when the leaves start to turn --
and the next year's budget projections are due :-)

Tom Kauffman
NIBCO, Inc
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