SAN data rates and performance
A reader wrote to ask: "Combining data means consolidating the I/O rate. Does SAN have an aggregate I/O rate at which point the performance is drastically reduced? I realize that there are probably enough paths, but it does not indicate nor have a way of indicating what the peak demand of I/O is."
"Our switches [and those of most other SAN manufacturers] are, generally, non-blocking so there is no bottleneck in the SAN superstructure. However bottlenecks can and do occur at either end of the switch, depending on the setup (too many SCSI disks on one FC port or slow HBA/driver/OS combo not able to max throughput on FC port)."
There are ways (such as Iometer) of getting the switch throughput data in bits/bytes. However, the "peak demand" comes from the client side and is limited not by the switch but by the bottlenecks that occur if the SAN is not set up or running properly.
To find out more about Intel's Iometer go to this searchStorage.com Administrator Tip: http://searchstorage.techtarget.com/Tips/searchStorage_Tips_Single_Listing_Page/1,286392,499591,00.html
About the authori: Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.
This was first published in January 2001