Storage Area Networks For Dummies®

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Part III: Using Advanced SAN Features
limiting factor. The same holds true for the backup server itself. Make sure
that your backup server can handle the load of backing up all the servers in
your environment.
Always use a server with lots of memory and very fast disks as your backup
server. The more memory a backup server has, the more data can be cached
on its way to the tape drive. The faster the disk your backup server uses, the
faster it can write and read the data it compresses (using its disk as temporary
storage) before sending it off to tape.
Determining backup speeds
If you back up over a LAN, you should always try to schedule backup during
off-hours when the LAN is not being used for production work. The same can
hold true for a SAN as well.
In SAN-backup solutions, it’s preferable to use a separate SAN connection for
backup. If your servers have two host bus adapters (HBAs) connected to the
SAN for disk access, you can dedicate a third adapter to backup. Then you can
run backup jobs across the SAN during normal business hours because the
backup data stream won’t affect production. Using two HBAs is fine as well, so
long as you dedicate only one of them to backing up data to a shared SANattached
tape library. You can zone the SAN to force this to happen. (See
Chapter 5 for more on zoning.)
Table 9-2 lists common network types, the maximum theoretical throughput,
and the typical throughput during backup if the network is dedicated for that
purpose. Keep in mind that if you’re also running other applications over
a LAN while you’re backing up, your backup speeds will decrease because
of congestion on the LAN. Notice that the typical throughput of a 1GB SAN
is much faster than the typical throughput of a 1GB 1000Base-T LAN. Both
networks run at the same speed, but the vastly faster Fibre Channel protocol
allows for a huge difference in backup speed over an Ethernet network.
Table 9-2
Typical Backup Speeds
Network Type Max Throughput Typical Throughput
10Base-T 3.6GB per hour 2GB per hour
100Base-T 36GB per hour 15–20GB per hour
1000Base-T 360GB per hour 160–200GB per hour
2-Gbit Fibre Channel 720GB per hour
540GB per hour
SAN
4-Gbit Fibre Channel
SAN
1440GB per hour 1080GB per hour