2Gb Fibre Channel – Determine Maximum Throughput Speed

With storage area networks (SAN) performance issues sometimes arrise.  Knowing the maximum throughput speed of your network is key to remove it as a possible bottlekneck.  Bellow I will outline the required calculations for determining the maximum throughput speed of 2 Gigabit Fibre Channel.

Calculation Rules
Network Speeds = Always in Bits
Storage/Disk Values = Always in Bytes
Files = Always in Bytes

1 nybble = 4 bits
1 word = 16 bits
8 bits = 1 Byte
1024 Bytes = 1 Kilobyte
1024 KB = 1 Megabyte
1024 MB = 1 Gigabyte

Calculating Maximum Throughput for 2 Gigabit Fibre Channel in MegaBytes
2 Gigabits = 2/8bits = 0.25 GigaBytes
0.25 GigaBytes x 2 (2 HBAs) = 0.5 GigaBytes
0.5 x 1024 = 512 MegaBytes/sec throughput or 256 MB/sec per HBA.

Depending on the monitoring software used performance numbers may not be in MB format. Bellow I’ve broken down the values for each common throughput value.

256 MegaBytes/sec =
262,144 KiloBytes/sec
268,435,456 Bytes/sec
2,147,483,648.00 Bits/sec
33,554,432 Bits/sec

Since FC speeds have tripled since I wrote this post an update is in order. Bellow I’ve outlined speeds for 4Gb and 8Gb FC.
4Gb = 512 MB/s
8Gb = 1024 MB/s

Now that we have determined the maximum throughput of each HBA we need to rule out any bottlenecks found in the server itself or in the SAN fabric.  HBA throughput speed is directly impacted by the bus speed of each HBA as well as whether the switch ports utilized by either the storage array FA’s or the HBA itself are dedicated bandwidth or over subscribed ports.

…. brain dump in progress