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FCArray RS/12 performance problems

Rodolphe Pineau
Occasional Contributor

FCArray RS/12 performance problems

I have a performance problem with my array.
I have 4 drives (73GB each) configured as RAID0.
all drives states say
Nego. Transfer Speed : 80MB/Sec
Nego. Bus Width : 16

I configured the controller for 40MHz (and the configuration window says 80MB/s for all the channels) and 16 bit on all scsi channel.
BUT .. when I ask for the controller information it says bus speed : 20MB/Sec
and all my speed test confirm this 20Mb/Sec limit.
if on the controller view i double click on the "processor device" to get the info .. the device state says :
Transfer speed : ASYNC
BusWidth : 8 bit (narrow)

Why ?!?!?!?!

and if I double click on the scsi controller:
Transfer Speed : ASYNC
BusWidth : 16 bits (wide)

I don't see any place to change this configuration.
And I have set all channel to 40MHz (80MB/Sec), 16 bits (wide)
So I don't expect to get the full 80MB/s but a least something close and certainly not a poor 18Mb/s as all my test shows.
Anyone has any idea of how to force/set the speed to an actual 80MB/s ?

Thank you
Marino Meloni_1
Honored Contributor

Re: FCArray RS/12 performance problems

negotiation speed is the speed of the bus (read clock bus)
the throughput is the speed that the data can reach reading or writing, this is not depending only of the bus speed (that may limiting is if lower) but is usualy limited by the write process on hdd, and read process on the source of the data.
do not mix both value.

The Bus width should be 16 bits, set in the bios of the raid controller under scsi controller settings, but if you have some problem with some pin of the scsi cables, it may negotiate at 8 bit, using only the 8 lower bits of the scsi bus, this will reduce the bandwith x2, if it is set to 80MB/s, switching from 16 to 8 bits, will end up in a max bandwith of 40 MB/s, this will take place at boot up, during the negotiation fase between the HBA and the RS/12 controller.

Rodolphe Pineau
Occasional Contributor

Re: FCArray RS/12 performance problems

This is a FC array so the scsi controller is in the array.
I'm accessing the array over fiber channel (2 gigabit link), not over a scsi card, which mean the CPU and the scsi controllers are together on the same pcb board inside the array (RAID controller inside the RS/12 FC so not "bios" setup as it's a fiber channel array).
The scsi controller indicate a negotiated speed of 80MB/s (40MHz 16bit LVD mode) with all the drive.
but for some reasons it seams the CPU on the FC raid controller communicate in a slower mode as stated in my initial post.
Marino Meloni_1
Honored Contributor

Re: FCArray RS/12 performance problems

Sorry, apologies for the error.

You can only set the speed and bandwidth at the controller level, here you can lower down the max speed of the negotiation, but default is the highest 40 MHz, 80 MB/s and 16 bits.

Now when the system boot up, there is a negotiation taking place between the controllers and the disks, (Do not remember if the monitoring component is also on the SCSI bus, but it may be, check if you have it on id5 - usually).
If one of the components of the bus has a pin bent, the bus may negotiate at 8 bit bandwidth, in this mode; the data are flowing at a lower speed but still can work.

So my suggestion is to open the box, check all the backplane for a bent pin, and eventually reduce to the lower the amount of disk on the bus, and see if you identify the cause of the bus not negotiation at full speed