One of the best ways to perform backups is to install a completely separate network to
carry all the backup traffic. However, many people do not have the funding
necessary to set up such a network, so they need to be careful about how their backup
system influences the network that it shares. There are a few different things that backup
products can do to minimize their impact on the network, whether it is a private one for
backups or the corporate backbone.
Keep Backup Traffic at the Subnet Level
One of the best ways for a backup product to reduce the amount of traffic that goes
between networks is to distribute the backup devices to the subnet level.
Keeping backup traffic on its local subnet results in two benefits. First, backup
traffic is distributed, so that no single subnet sees all the traffic. The overall
impact to the internal customer (who also is trying to use the corporate intranet) is
therefore reduced. The second benefit is that the overall throughput of the backup
system will be able to scale with the network as the network grows by the addition of
subnets. Consider the drawing in Figure 1. There are six different subnets (100.10–100.15), each of which is switched
10 MB (switches not shown). Each of the switches is plugged into a router, which also is
plugged into the 100.1 subnet, where the backup server resides.
Figure 1. Network backup data paths
A typical, network-based backup system causes data to flow in the manner illustrated
by the data path on the left. The data path represented by the left-side dotted line
shows that the data goes over the 100.10 subnet, the router, and the 100.1 subnet to the
backup server. If all six subnets are backed up that way, the total backup throughput
could be no higher than the speed of the 100.1 subnet or the router because all traffic
must go through them. The result is that the backup system never streams the backup
However, if the backup software supports remote devices, the backup traffic can be
localized to the subnets, as illustrated on the right. Even without taking advantage of
switching technologies, the backup system now has an overall throughput of 6 MB/s
instead of 1 MB/s.
Use Client-Side Compression
Backup software products also can use client-side compression to reduce network traffic. This
means that files are compressed on the client before they are sent across the network.
This is very CPU-intensive on the client end, but the amount of data that actually goes
out on the network can be greatly reduced. If the system CPUs are fast and the network
is slow, this can improve overall backup throughput and reduce total backup time.
Using client-side compression can slow down restores as well. How much restores
are affected varies with the product and the nature of the systems being backed up.
Before using compression, test to see how much it affects restore performance. It may
be too great a sacrifice.
Another feature that is difficult to find in backup software products is called
tling and can help reduce the effect of the backup traffic on the
overall network. Some products allow the administrator to throttle a backup client, that
is, to specify how many megabits per second a backup client can send out on the network.
That way, even on a 100 Mb network, the backup system would use only a prescribed
percentage of the total bandwidth, since that’s what it was told to do. This slows down
the backups, of course, but the people trying to use the network will surely appreciate
Storage area networks, as shown in Figure 2, present several
advantages when used with a backup system. A SAN:
Provides scalable storage devices, which can be shared regardless of
Grants faster data migration, allowing storage redeployment in a highly
available, distributed, or centralized environment
Supports higher levels of I/O throughput
Allows increased performance on backup and restore tasks
Contributes to better host connectivity, due to offloading the LAN from storage
Promotes sharing of both storage and backup devices across the enterprise
When considering SAN technology in light of the backup and recovery industry, it is
the ultimate network traffic-reduction method. It allows SAN-connected hosts to perform
LAN-free backups, taking advantage of the recent
advancements in CPU and memory usage reduction. It does all this while allowing maximum
utilization of large libraries. If you have a large environment, and especially if you
have very large servers, you definitely should find out which backup applications
support LAN-free backups.
Figure 2. Connecting any type of peripheral via a SAN