Calculating the Bandwidth Availability

Bandwidth availability is based on the following:

• Number of LUNs (logical unit numbers)

• Number of physical disks per LUN

• RAID level of the LUNs

• How the LUNs are gathered into storage pools

• The nature and redundancy of the Fibre network

As a rule of thumb, consider that a single Xserve RAID controller, after file system overhead, can transfer roughly 80 to 100 MB of user data per second (160 to 200 MB per Xserve RAID system). If your SAN must support an application running on multiple clients that requires specific throughput on each client, you can use this number to estimate the number of Xserve RAID systems necessary to support the aggregate transfer rate.

This formula will generally aggregate upward to the current maximum size of an Xsan volume, which is 1024 TB. This means, for example, that four Xserve RAIDs, with eight seven-drive LUNs, combined into a single storage pool, are currently yielding a total bandwidth availability of 640 to 800 MB/s.