152 IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning
The SAN fabric switches in-between. The switches are the heart of the SAN network.
The connection medium, which consists of cables, and the host adapter cards on each
end (Qlogic, Emulex, or JNI), that reside in the server and the storage.
Notice each server is at least dual attached to the SAN for availability and load balancing. The
storage devices—the DS6000 and the tape library—have multiple SAN connections for
availability and performance.
This is just one example of a SAN, and there are a myriad other ways to create a SAN with
different types and numbers of servers, storage devices, and switches.
5.5.2 Benefits of a SAN
One of the biggest benefits of a SAN is centralized storage. Before SANs were available, it
was common for servers in a data center to each have their own dedicated storage. Backups
were difficult because the servers had to use their own tape drives, or backup over an
Ethernet network. Sharing a tape drive could be possible, but usually meant moving the tape
drive from one server to another, and reboots were required to attach the tape drive.
Re-assigning disk storage meant making cable changes and possibly moving storage or
Some of the benefits a SAN offers are:
The ability to assign and un-assign a large (TB) amount of storage to a host with just the
click of a mouse. No cabling changes required.
Hosts can share storage for failover environments, or actually work on the same data
using software that provides locking protection.
Availability: Multiple connections between servers and storage.
Performance: Each Fibre Channel adapter runs at 100 MB/s or 200 MB/s.
LAN congestion is reduced by moving backups off the LAN and onto the SAN.
Faster backups: It is even possible to implement
server free backups, which copy data
directly (at the block level) from the DS6000 to tape with no load on servers.
Increased distance (10 km +) between servers and storage for convenience and security.