[Veritas-bu] Sizing of media by number of tape drives

As a starting point, apply some elementary capacity planning guidelines
to calculate the theoretical maximum number of tape drives per network
segment.

First, you need to know the maximum rate of accepting data of your drive
in megabytes per second. You should use the manufacturer's claim unless
you have better data. Let's call that "Tape Rate".

Next, you need to know the maximum capacity (bandwidth) of the SAN path
from the media server supplying the data to the drive. This must reflect
the most restrictive component (bottleneck) from the media server to the
drive, whether that's an HBA, an ISL (Inter-switch link), a SCSI Bridge
or whatever. We'll call that "Bandwidth".

Here's the formula to use to calculate the conservative optimum number
of drives you should use:
                                        Bandwidth
Number of drives = INTEGER part of(     ----------- )
                                        Tape Rate

Or, if your email system eats this formatting:

The number of drives should not exceed the integer portion of the
maximum bandwidth of any SAN path divided by the rate at which the tape
drives will accept data.

That said, you may find that you can get away with up to 2x the number
of drives calculated in this manner, especially if the Tape Rate is
vendor specified based on counting on compressible data (text) and you
are archiving non compressible data.

Another factor in your problem is the ability of your media server to
supply data to the tape drive at the maximum rate. If your media server
is receiving data streams from the IP network and it is not multiplexed
and not using multiple gigabit adapters, you are not likely to be able
to keep up with the potential capacity of the newer LTO2/LTO3 or AIT3+
tape drives, so you could increase the number of drives per SAN path if
you found that you are not using the capacity of the drive.

Good practice would dictate that you periodically (or continuously if
you have the tools) monitor the effective rate of throughput to the
drives. You could find the best configuration experimentally by
recording the actual data rates at the switch ports connected to the hba
of your system then incrementally add tape drives. When the rate
flattens, back off by one, and you will have your optimum configuration.

It really is easier than it sounds, but making flat recommendations for
all situations isn't recommended.

Good luck,

Mickey Baker
Senior Consultant 
GlassHouse Technologies


-----Original Message-----
From: veritas-bu-admin AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu] On Behalf Of
ida3248b AT post.cybercity DOT dk
Sent: Tuesday, January 04, 2005 12:00 PM
To: veritas-bu AT mailman.eng.auburn DOT edu
Subject: [Veritas-bu] Sizing of media by number of tape drives

Hello All

I have tried to find a guide lines for sizing Solaris and AIX media
servers 
by the number of attached tape drives.

I have gotten a internal work document from Veritas but it dosn't
contain the 
enterprise tape drives we are using (STK9840 and STK99940).

We have 8 STK9940B drives that I want to get streaming.

We have 2 AIX 5.2 Media servers and 1 Solaris Master/media server that
shares 
these 8 tapes drives, but I would each media server to be able to stream
all 
8 drives.

Does somebody on list have a set of guide lines ? 

or suggestions/ideas ?

Regards
Michael

--
Cybercity Webhosting (http://www.cybercity.dk)

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