LTO-2 and LTO-3 switch grouping

2006-08-29 11:52:40
Subject: LTO-2 and LTO-3 switch grouping
From: Robin Sharpe <Robin_Sharpe AT BERLEX DOT COM>
Date: Tue, 29 Aug 2006 11:51:06 -0400
Hi All,

We have the good fortune to be adding four LTO-3 drives to our STK L700
library.  It currently has 14 LTO-2 drives, attached to two Brocade 3800
(2Gpbs, 16-port) switches.  All drives are IBM FC.  I'm trying to figure
out the best approach to zone these drives.   We currently use port zoning
on these switches, but as part of this upgrade, we will enable the WWN
feature on the L700, and migrate the switches to WWN zoning.  Here are my

Current config:  (4) HBAs on the TSM server for tapes
      On switch1,
            hba1 has (3) LTO-2 drives
            hba2 has (4) LTO-2
      On switch2,
            hba3 has (3) LTO-2 plus (3) DLT8K  (the DLT's are going away
with this upgrade)
            hba4 has (4) LTO-2

The DLT's are never used, so they have no real impact.  I know the hba's
with (4) LTO-2 are over-committed, and although I have no direct evidence
of a problem, my gut feeling is that it is a bottleneck at times.  I have a
few FC cards that I can add.  There are two open PCI slots on the TSM
server... with some more reconfiguration, I can free up two more.  This is
an HP rp7410 server, and all PCI slots are 66Mhz x 64 bit capable, with
throughput of 530MBps.... so, I can put FC adapters anywhere with no
throughput concerns.

What I'm considering:
- IF I can add four more HBAs (best case - no over-commitment),
      On each switch,
            hba1 with (1) LTO-3 and (1) LTO-2
            hba2 with (1) LTO-3 and (1) LTO-2
            hba3 with (3) LTO-2
            hba4 with (2) LTO-2

-If I can only add two HBAs (less reconfiguration),
      On each switch,
            hba1 with (1) LTO-3 and (1) LTO-2
            hba2 with (1) LTO-3 and (2) LTO-2  (44 MBps over-commitment)
            hba3 with (4) LTO-2  (24 MBps over-commitment)

My "over-commitment" calculations are based on 2048 Mbps / 8 bits per byte
= 256 MBps throughput per switch port.
I'm wondering if there are any issues with zoning LTO-2 and LTO-3 to the
same HBA... will either one monopolize the port, or will play nice
Any comments are greatly appreciated!

Robin Sharpe
Berlex Labs

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