Qlogic FastLinQ 3400 Series, User Manual

Page: 244 / 287

15–QLogic Teaming Services
Application Considerations
216 83840-546-00 E
Because there are four client servers, the backup server can simultaneously
stream four backup jobs (one per client) to a multidrive autoloader. Because of the
single link between the switch and the backup server; however, a 4-stream
backup can easily saturate the adapter and link. If the adapter on the backup
server operates at 1Gbps (125MBps), and each client is able to stream data at 20
MB/s during tape backup, the throughput between the backup server and switch
will be at 80 MB/s (20 MB/s x 4), which is equivalent to 64% of the network
bandwidth. Although this is well within the network bandwidth range, the 64%
constitutes a high percentage, especially if other applications share the same link.
Load Balancing and Failover
As the number of backup streams increases, the overall throughput increases.
Each data stream, however, may not be able to maintain the same performance
as a single backup stream of 25 MB/s. In other words, even though a backup
server can stream data from a single client at 25 MB/s, it is not expected that four
simultaneously-running backup jobs will stream at 100 MB/s (25 MB/s x 4
streams). Although overall throughput increases as the number of backup
streams increases, each backup stream can be impacted by tape software or
network stack limitations.
For a tape backup server to reliably use adapter performance and network
bandwidth when backing up clients, a network infrastructure must implement
teaming such as load balancing and fault tolerance. Data centers will incorporate
redundant switches, link aggregation, and trunking as part of their fault tolerant
solution. Although teaming device drivers will manipulate the way data flows
through teamed interfaces and failover paths, this is transparent to tape backup
applications and does not interrupt any tape backup process when backing up
remote systems over the network.
Figure 15-10 shows a network topology that
demonstrates tape backup in a QLogic teamed environment and how smart load
balancing can
load balance tape backup data across teamed adapters.
There are four paths that the client-server can use to send data to the backup
server, but only one of these paths will be designated during data transfer. One
possible path that Client-Server Red can use to send data to the backup server is:
Example Path: Client-Server Red sends data through Adapter A, Switch 1,
Backup Server Adapter A.
The designated path is determined by two factors:

Client-Server ARP cache; which points to the backup server MAC address.
This is determined by the QLogic intermediate driver inbound load balancing
algorithm.

The physical adapter interface on Client-Server Red will be used to transmit
the data. The QLogic intermediate driver outbound load balancing algorithm
determines this (see
“Outbound Traffic Flow” on page 190 and “Inbound
Traffic Flow (SLB Only)” on page 190 .