Re: LTO-2 and LTO-3 switch grouping

2006-08-29 12:11:23
Subject: Re: LTO-2 and LTO-3 switch grouping
From: "Smith, I (Ian)" <Ian.Smith AT RABOBANK DOT COM>
Date: Tue, 29 Aug 2006 17:07:16 +0100
Ensure the PCI slots do not share internal BUS bandwidth. You may end up
with issues there- I moved to dual port PCIe cards for the internal
bandwidth to run many LTO3 drives. Is the server really only PCI, or are
they PCI-X slots?

There is no issues running LTO2 and LTO3 on the same HBA.

I have looked into the fabric throughput to actually see the speeds-
they can be very high- near the theoretical maximums if you are using
format=drives or UTRIUM3/2C. Any type of oversubscription/commitment can
cause severe impact on streaming performance.

Ian Smith
SAN/TSM Specialist
Hitachi Data Systems Certified Professional
IBM Tivoli Storage Manager Certified Consultant

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Robin Sharpe
Sent: 29 August 2006 16:51
Subject: [ADSM-L] LTO-2 and LTO-3 switch grouping

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
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 thoughts...

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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