FC slower than SCSI?

[Col_G]

Hi.

Im in the process of building a new NBU 7 environment to replace our aged nbu6 setup.. 

Ive been doing some basic testing when ive been able to get time to use our tape library (i500) and have noticed that backing up to the library over FC is quite a bit slower than backing up the same data to a scsi attached drive. (ie 40mb/s vs 20mb/s)

Should this be the case or is there potentially something not quite right with the FC config?.. its a basic setup with a single 4g link from a QLE2462 into the blade on the back of a quantum i500 with 3 drives. there is no channel zoning or other config done for the FC side and HBA drivers are up-to-date.

Any words of wisdom appreciated.

Thanks

[alazanowski]

Just to confirm, are you saying that there is a limit of 1 4g link between the system and then that link is shared for all 3 drives? Or does each drive maintain 1 4g link into the SAN switch? 

Alot of speed change can occur depending on how your buffers are set for tape. Assuming this is an *nix system, then i recommend setting the buffer size to 256k and number of buffers to 64 (pending that you have enough memory). You can find out how to do these in the performance tuning guide. If you need additional assistance, just let me know and I can help walk you through it. (This actually isn't a bad step to perform whether you are running scsi connection or fiber). 

Also, is that FC connection on the server sharing any other zoning? Are you allocating some other I/O intensive connection to the same hba port? As a guideline, you should not share tape and disk out of the same hba port.

[Col_G]

Hi Thanks for your reply.

The server (win2k8 64 8-core 32gb ram) has a single 4g connection into the fc "blade" on the back of the library which acts as the control path and switch for the three LTO4 drives.. i cant see ever needing to drive all three drives through netbackup at once, its more for flexibility than anything else. There is nothing else on the FC infrastructure its just point to point really.

I shall dig out the buffer settings for the NBU6 server we have. i assume the same rules apply?