Broadcom Teaming Services: Broadcom NetXtreme II® Network Adapter User Guide
file:///C|/Users/Nalina_N_S/Documents/NetXtremeII/English/teamsvcs.htm[9/5/2014 3:45:08 PM]
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 10
shows a
network topology that demonstrates tape backup in a Broadcom 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 Broadcom
intermediate driver inbound load balancing algorithm.
The physical adapter interface on Client-Server Red will be used to transmit the data. The Broadcom intermediate
driver outbound load balancing algorithm determines this (see
Outbound Traffic Flow
and
Inbound Traffic Flow (SLB
Only)
.
The teamed interface on the backup server transmits a gratuitous address resolution protocol (G-ARP) to Client-Server Red,
which in turn, causes the client server ARP cache to get updated with the Backup Server MAC address. The load balancing
mechanism within the teamed interface determines the MAC address embedded in the G-ARP. The selected MAC address is
essentially the destination for data transfer from the client server.On Client-Server Red, the SLB teaming algorithm will
determine which of the two adapter interfaces will be used to transmit data. In this example, data from Client Server Red is
received on the backup server Adapter A interface. To demonstrate the SLB mechanisms when additional load is placed on the
teamed interface, consider the scenario when the backup server initiates a second backup operation: one to Client-Server
Red, and one to Client-Server Blue. The route that Client-Server Blue uses to send data to the backup server is dependant on
its ARP cache, which points to the backup server MAC address. Because Adapter A of the backup server is already under load
from its backup operation with Client-Sever Red, the Backup Server invokes its SLB algorithm to
inform
Client-Server Blue
(through an G-ARP) to update its ARP cache to reflect the backup server Adapter B MAC address. When Client-Server Blue
needs to transmit data, it uses either one of its adapter interfaces, which is determined by its own SLB algorithm. What is
important is that data from Client-Server Blue is received by the Backup Server Adapter B interface, and not by its Adapter A
interface. This is important because with both backup streams running simultaneously, the backup server must
load balance
data streams from different clients. With both backup streams running, each adapter interface on the backup server is
processing an equal load, thus load-balancing data across both adapter interfaces.
The same algorithm applies if a third and fourth backup operation is initiated from the backup server. The teamed interface
on the backup server transmits a unicast G-ARP to backup clients to inform them to update their ARP cache. Each client then
transmits backup data along a route to the target MAC address on the backup server.
Fault Tolerance
If a network link fails during tape backup operations, all traffic between the backup server and client stops and backup jobs
fail. If, however, the network topology was configured for both Broadcom SLB and switch fault tolerance, then this would
allow tape backup operations to continue without interruption during the link failure. All failover processes within the network
are transparent to tape backup software applications. To understand how backup data streams are directed during network
failover process, consider the topology in
Figure 10
. Client-Server Red is transmitting data to the backup server through Path
1, but a link failure occurs between the backup server and the switch. Because the data can no longer be sent from Switch #1
to the Adapter A interface on the backup server, the data is redirected from Switch #1 through Switch #2, to the Adapter B
interface on the backup server. This occurs without the knowledge of the backup application because all fault tolerant
operations are handled by the adapter team interface and trunk settings on the switches. From the client server perspective,
it still operates as if it is transmitting data through the original path.
Figure 10: Network Backup With SLB Teaming Across Two Switches
