Changing/Tuning Block Size/transfer size in a QLogic HBA in Windows 2008

SAN performance depends on many factors including workload, application tuning, server and SAN hardware, HBA settings, switch settings, and storage array configuration.
With Windows 2003/2008 and HBA drivers,given a sufficient workload demand on the storage array including one or more hosts and applications and default HBA queue depths, the host I/O latencies might be higher which will cause performance issues on storage box. To overcome this situation,one tuning option available with the HBA drivers is to tune the HBA queue depth to lower values. Workload latencies, throughput and IOPs may see improvements with reduced queue depth values as the load on storage box will be less. There is a new option available with the latest release of Qlogic HBA drivers, which gives the ability to tune the data transfer size to values smaller than the default of 512 KB. 

Older HBA have a physical limitation and cannot handle block size bigger than 256 KB or 512KB. Newer HBA, even if they support 2048 KB (2 MB) Block size, default is set to/limited to 512 KB.In order to change the transfer block size limit, QLogic driver, version 9.1.8.28 or later, has been enhanced to allow the ability to optionally tune the data transfer size to less than 512 KB. The CLI command called QLogic FC Utility : qlfc.exe 


Usage:The user can open a DOS prompt in administrator mode typing in the Run /Search line CMD then press the CTRL + SHIFT + ENTER key, or right click on the CMD icon and select Run as Administrator .

qlfc [-list] [-tsize [/fc | /fcoe [/set [64 | 128 | 256 | 512 | 1024 | 2048 | default] ] ] ]
    -list                   List all HBA instances
    -tsize                  Show current transfer size setting for both fc & fcoe
    -tsize /fc              Show current transfer size setting for fc
    -tsize /fcoe            Show current transfer size setting for fcoe
    -tsize /fc /set value   Set transfer size parameter for fc
    -tsize /fcoe /set value Set transfer size parameter for fcoe

Note:
 * QLFC.EXE      - Command line utility (32-bit version)
 * QLFCx64.EXE   - Command line utility (x64 version)
 * QLFCia64.EXE  - Command line utility (IA64 version)

Examples:
    c:\>qlfc -list    
    c:\>qlfc -tsize    
    c:\>qlfc -tsize /fc  
    c:\>qlfc -tsize /fc /set 256    
    c:\>qlfc -tsize /fc /set default
This will allow the user to see the actual values and allow the user to change these values.In Windows 2008 one needs to run this command with Administrator right.After changing the parameter a reboot is required.