Specifications
DATA CENTER BEST PRACTICES
SAN Design and Best Practices 62 of 84
Figure 41 shows a typical implementation of an in-line virtualized storage solution. The host or VM accesses
storage via a storage controller (shown on top) through the storage network. The orange arrows indicate data
access to and from the storage controller. The storage controller typically controls all access to the physical
storage, shown on the right (and indicated by the blue arrows). This creates a very exible storage solution,
because logical LUNs can be striped across several physical arrays to improve performance, and logical LUNs
can be manipulated completely transparently to the host or VM.
fig38_SAN_Design
Storage
Network
Host/VM Physical
Storage
Storage
Controller
(in-line)
Figure 41. Typical implementation of an in-line virtualization storage solution.
The major benet of this type of storage virtualization is that storage can now be provisioned in units of capacity
(500 gigabytes or a terabyte) rather than physical LUNs. This is a rst step toward viewing storage as a service
instead of as physical units. VM provisioning now becomes less complex and easier to automate. Look into
products such as IBM SAN Volume Controller, Hitachi Data Systems Universal Storage Platform, EMC Invista,
and HP SAN Virtualization Services Platform (SVSP) for information about how these products work.
Design Guidelines
•Each storage controller in an in-line solution serves as both an initiator and a target.
•ISL utilization increases with in-line virtualized storage. Make sure that you have enough ISL bandwidth to
handle the increased load.
•There is also the possibility that the in-line storage heads will communicate through Fibre Channel or generate
many more SCSI control frames to manage their attached storage, which can contribute to frame congestion.
You may need to increase the number of buffers at the ports that connect to the storage controller to
accommodate this behavior.
•It is much more difcult to determine initiators and targets with in-line virtualized storage. Since they are on
the same switch, be careful about deploying tools such as Port Fencing.
Monitoring
•Bottleneck Detection is very useful in determining latencies associated with virtualized storage.
•Brocade FOS features such as Advanced Performance Monitoring and Top Talkers are helpful in looking at
high-trafc-usage ows.