Re: How do you keep a 3590E busy enough?

Hi,

to get maximum performance of the 3590 drives you
could play with migration parameters.

1) Avoid backup directly to tape, or your network
  communication (even if you have Gigabit or ATM,
  because of the protocol and communication
  overhead) will be the bottleneck. Use a diskpool
  for buffering

2) Set your migration parameters with a big HI MIG
  and a low LO MIG (like 85/90 and 30/25) so you
  are sure that when tapes are mounted, they spend
  most of the time writing and lowering the level
  of occupancy of the diskpool.

The most significant aspect on these high performance
drives is to assure they will keep writing most of
the time when you mount a volume.

It also depends on the server box and the disk
technology, because if the drives are faster than
disk or the throughput of the server, the 3590
will wait for I/O and you won4t good
performance.

regards,
Rodrigo

From: John Schneider <jdschn AT IBM DOT NET>
Reply-To: jdschn AT ibm DOT net
To: ADSM-L AT VM.MARIST DOT EDU
Subject: How do you keep a 3590E busy enough?
Date: Wed, 3 Nov 1999 10:31:47 -0600

Greetings,
    I must be missing something obvious, so if I am, you can just flame
me and I will cheerfully accept your harassment.  It has certainly
happened before :-).
    How is it that you keep a 3590E tape drive writing at 36MB/sec using
ADSM? If I understand ADSM right, when a client is backing up to tape
drive, that client is the only thing that writes to that drive.  And the
way the clients seem to work, only one client session writes to an
individual tape drive at a time.  And only one filesystem (on AIX, for
example) is read by the ADSM client software at a time.  That means the
usually only one disk is writing across the network to one tape drive.
    On a modern IBM Scorpion disk with no other load on it, you can get
about 9MB/sec transfer rate, 12MB/sec burst.  So if one disk is sending
data to a single tape drive, the tape drive cannot possibly write data
faster then 9-12MB/sec, right?   And that assumes that the network is
not the bottleneck, or the client and the server are the same machine.
    We are currently using DLT7000 drives, which typically only write at
5.5MB/sec, and having trouble accomplishing the backups in a reasonable
period of time.   We were looking in to 3590 drives for the tremendous
speed they can provide, but how can we configure ADSM to use it?
    For some of our smaller client backups, we could send the data to a
disk pool, then migrate it to tape, but that doesn't really cure the
problem, since then a disk pool volume reading at 9MB/sec is trying to
drive a 36MB/sec drive, which can't keep it busy.  And we nightly back
up a 400GB database, so we have to go directly to tape for that backup,
we can't throw 400GB of intermediate disk pool at it!  Would even a
small amount of disk pool help?
    Is there any way to cause ADSM to write several client sessions to a
tape drive shared between them?  Or a way to have multiple disks to all
send data to the same tape drive at once?
    Since there are a number of you out there who have these 3590
drives, you must have done this before.  Any hints about what the method
is?  Or a clear explanation of what I don't understand?

Thanks in advance,

John Schneider

***********************************************************************
* John D. Schneider   Email: jdschn AT attglobal DOT net * Phone: 636-349-4556
* Lowery Systems, Inc.
* 1329 Horan                  Disclaimer: Opinions expressed here are
* Fenton, MO 63026                   mine and mine alone.
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