twa driver and 3ware 9690SA issues

[Scott Long]

Josh Paetzel wrote:
> This is somewhat of a repost from questions@, and I'm currently engaged 
> with 3ware about this issue.
> 
> I have several 3ware 9690SA SAS RAID controllers.   This item is very 
> similar to their 9650SE controller.  It uses the same firmware and 
> driver, the difference being it can handle SAS drives.  Up until this 
> point all of the arrays we've used with these drives have been RAID 1 
> arrays with 7200 RPM SATA drives, but recently we've started using 
> 15,000 MBA series Fujitsu SAS drives in places.
> 
> The arrays have always been detected as:
> 
> da0: <AMCC 9690SA-4I  DISK 4.06> Fixed Direct Access SCSI-5 device
> da0: 100.000MB/s transfers

This 100.000MB/s number is fictitious.  The driver is just filling in a
dummy value.  Filling in the real number would require the driver being
able to query the card for the negotiated bus speed.  I have no idea
if that's possible for TWA given the programming information that is
public for the card.

> 
> Which wasn't that much of an issue, as SATA drives aren't capable of 
> sustained sequential 100 MB/sec transfers anyways, but the SAS drives we 
> are getting are supposedly capable of 180 Megs/sec and I'm not seeing 
> it.  I'm unsure of how to eliminate caching from the equation, simple 
> tests like dd if=/dev/zero of=testfile bs=8m count=1000 seem to support 
> what dmesg reports by returning 96 Meg/sec transfer rates
> 

FreeBSD limits individual I/O segments through the CAM subsystem to
64K.  It can safely be raised to 128K via some patches that I have, and
you will see a corresponding improvement in performance.  I don't
believe that it can be safely raised above that for the TWA controllers.

Scott