AutoRAID 12H question

[Mark Jones_1]

Hi,

Does anyone know what the SDTR and WDTR settings actually do? Whilst it seems that these can have a negative impact on performance if not set correctly, I thought that these settings were used to negotiate synchronous data transfer requests and 'wide' data transfer requests respectively? If not set, I thought the negotiation would be determined by the host.

Clarification please.

Thanks, Mark.

[David Bell_1]

Mark,

From the user's and service manual of the Model 12H disk array:

Parity
NOTE! This command requires a SCSI Reset or power cycle to take effect.
Parity switches SCSI Parity on (default) or off for the primary array controller. When parity is on, it
enables error detection in the primary array controller.
SDTR
NOTE! This command requires a SCSI Reset or power cycle to take effect.
Synchronous Data Transfer Request. SDTR enables (default) or disables SCSI SDTR (Synchronous Data
Transfer Request). SDTR controls the data rate on the SCSI bus used by the host and the array. SDTR also
determines the negotiation protocol of the host. If SDTR is enabled, the array will initiate negotiation
protocol; if disabled, the host will initiate negotiation protocol. In either case, the disk array will always
respond to any requests made by the host.
WDTR
NOTE! This command requires a SCSI Reset or power cycle to take effect.
Wide Data Transfer Request. WDTR controls whether or not the additional eight bits on a wide bus will be
utilized in most data phases of a SCSI command. WDTR also determines the negotiation protocol of the
host. If WDTR is enabled, (default) the disk array will initiate for negotiation for wide transfer. If WDTR is
disabled, the host will initiate negotiation protocol. In either case, the disk will always respond to any
requests made by the host.

HTH,

Dave

[Mark Jones_1]

Indeed it does. I have read it. If you have these settings disabled, will it really affect performance? Or will the host negotiate the synchronous and wide transfer settings itself?

Thanks again, Mark.

[David Bell_1]

Mark,

While I have not personally tried this, it should not affect performance. It simply means that any I/O from host to array should utilize the SDTR/WDTR via the host instead of the array. Internally, the array will handle things differently regardless of whether or not this is disabled. It only pertains to the host/array communication. I'm not sure what you're utilizing as a host, however, be sure if you're using HP-UX and you decide to do this, you get the latest WSIO SCSI patch prior! For HP-UX 11.00, the "Best" patch is PHKL_26452 and the "Latest" is PHKL_27003. Both include script enhancements for WDTR/SDTR.

HTH,

Dave

[Mark Jones_1]

Thanks for the input.

Where do you think I will find a definitive answer to the performance question? I have tried looking in all sorts of places, but to no avail. And, if I decide to reset these back to the defaults (enabled) can this be done 'on the fly?'

Thanks again, Mark.

[David Bell_1]

Mark,

I too spent some time looking around for information on this. I had no better luck in finding much on WDTR and performance. I'm not sure of your environment and what you're attempting to accomplish. If this is performance related, you might want to look at the following:

http://www.hp.com/cposupport/information_storage/support_doc/lpg75003.html

This is on the "write working set".

Sorry I couldn't be of more assistance,

Dave