ADSM-L

Re: SCSI Cards and 3590 Tape Drives

1998-09-11 16:42:16
Subject: Re: SCSI Cards and 3590 Tape Drives
From: Matt Cleland <adsmrus AT STLNET DOT COM>
Date: Fri, 11 Sep 1998 15:42:16 -0500
Hi Brandon..

Most of your questions are not really ADSM related, but more RS/6000
architecture and bandwidth related.  That said, I'll take a stab at a few:

1) SCSI cards vs. 3590 drives.  Since the maximum bandwidth of a SCSI-II FWD
bus is 20MB/s, and the 3590 can stream data at ~9MB second, you would be
oversubscribing the SCSI bus if you put three 3590s on a bus.  My personal
preference is to put 1 drive per adapter, but you can most likely get by
with 2 drives per adapter since you are somewhat limited by the H50s slot
count.

2) SSA loop configuration:  This is a complicated scenario, but the general
rule still applies:  More bandwidth is better.  Each SSA loop is rated at
40MB/s, with 2 loops on an adapter.  That said, it's simple math to
determine how you're dividing up your bandwith among the different spindles.
In your suggested configuration, you would have 24 spindles per loop, so
that gives you about 1.67 MB/s of bandwidth (on average) available per
drive.  That's not a whole heck of a lot, given the speed that the
individual drives are capable of.  I know that you won't be hitting all the
drives simultaneously, but you can see my point.
In your situation, you will have 3 drawers of SSA disks, that could be split
into a maximum of 12 separate loops.  I probably wouldn't go to that
extreme, but would certainly consider using more than one adapter / 2 loops.

Please feel free to call or email if you need some additional help.

--------------------------------------------------------------
Matt Cleland                            mcleland AT msiinet DOT com
Matt Cleland                            mcleland AT msiinet DOT com
IBM Certified Specialist - ADSM
Midland Systems, Inc.                   (618) 345-0864
St. Louis, MO                           (618) 346-1779 FAX


> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU]On Behalf Of
> Brandon Moore
> Sent: Friday, September 11, 1998 2:33 PM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: SCSI Cards and 3590 Tape Drives
>
>
> Fellow ADSMers:
>
> I need an answer to some of these questions:
>
> The h/w configuration of server:
> RS6000 H50 2-way 332 Mhz CPU's with a PCI based System I/O Bus
> 512 MB of RAM
> AIX 4.2.1
> Six 3590 Tape Drives connected to two SCSI F/W Differential
> Adapters, three
> drives per adapter.
> 436 GB of SSA DASD connected on one SSA Enhanced(Non-RAID) Adapters in two
> loops of 48 physical disks(9.1 GB SSA)
> ADSM 3.1.1.5 with 2500+ clients
>
>
>
> Which is faster(assuming the above Hardware configuration) in general?
>
>      One SCSI F/W Card with one 3590 Tape Drive
>
>           OR:
>
>      One SCSI F/W Card with three 3590 Tape Drives daisy chained...
> What if you were running migrations or multiple restores/backups to/from
> 3590 Tapes, you know ADSM-type stuff:
>
> Of these which would be faster?
>
>      One SSA Adapter(Two SSA Loops)
>
>           OR:
>
>      Two SSA Adapters(Four SSA Loops)
>
>           OR:
>
>      Four SSA Adapters(Eight SSA Loops)
>
> What if you had a large number of database reads/writes?
> What if your daily incrementals were more than your DISKPOOL
> allocation and
> you had to Migrations in the the middle of backup?
>
>
> Any thoughts would be appreciated...Thanks in advance
>
> Brandon W. Moore
> State Farm Insurance
> brandon.moore.hoq0 AT statefarm DOT com
>
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