One note to add:

I have a private backup network:  One VLAN for my production (Windows) servers and one VLAN for my Development (Unix, Sparc, Sun, etc) servers.

Will Tucker | Storage Administrator

Enterprise Technology Services

Manhattan Associates, Inc.

Direct +1 678.597.6644

Phone +1 770.955.7070

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wtucker AT manh DOT com

http://www.manh.com/

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The Supply Chain People®
Manhattan Associates

Will,

Questions like this vary greatly based on many factors.  In short, you're really the only one who can determine that.  Here are some basic guidelines I use.

1.  Most people probably use media servers to backup themselves.  This keeps large amounts of data off the network.  You need to figure out the maximum data transfer rate for your media server (system I/O), the maximum transfer rate of your source disks, and the maximum transfer rate of your tape drives.  In this case, the slowest one wins and is the best case number you can use.  You then figure out how much data you will backup for a full backup (worst case transfers), divide that by your best case transfer rate, and that will tell you how long it will take to do that backup. 

2.  For client backups to media or master servers over the network, you need to factor in the same things as above, but now the network traffic becomes another factor.  If you flood the LAN and have to dial things back to keep other users happy, it will affect how much you can effectively backup.

3.  Throttling the backups, locally or across the network, may need to be considered.  If you find running an all-out full backup on a client drives it into the ground where users complain, you'll need to factor in slower times as you restrict throughput or look into things like a dedicated backup network and interface.

4.  What is an acceptable backup window for your clients.  If you have 12 hours to backup 10 TB you need to make sure each of the pieces are capable of performing at a high enough level.  If it currently takes you 6 hours, you have room for more data.  If you are already at 12 hours then you need to find out which piece isn't keeping up and decide if you can change it.

As you can see, the number of tape drives or media servers may not be a factor.  If you can write 80MB/s to a tape drive but your source disks are only putting out 30MB/s adding more tape drives or media servers will not help you at all.  Do some testing of the individual piece involved in your backups and see where your weakest link is.  You should be able to figure out where you are limited from there.

Jeff

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Jeff Cleverley
Unix Systems Administrator
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