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List:       freebsd-scsi
Subject:    Re: Testing new mpr driver
From:       Borja Marcos <borjam () sarenet ! es>
Date:       2014-05-08 7:49:02
Message-ID: 4DB83981-0D4D-4484-BC89-4ED8C02DCD0F () sarenet ! es
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On May 7, 2014, at 8:45 PM, Kenneth D. Merry wrote:

> That's hard to say.  If you're using a 6Gb expander, you would have half of
> the available SAS bandwidth if you only connected four lanes from the
> controller to the expander instead of 8.  If you somehow have a 12Gb
> expander (it isn't obvious from the model number above what the expander
> speed is), then you would have the same amount of bandwidth.

Anyway, as far as I understand (SAS expanders perform link switching, right?) the \
actual speed will be limited by the end to end speed. As the disks I am using are \
SATA, not SAS, each lane would be anyway working at  6  Gbps instead of 12. 

> One thing that could be happening is you may have lower latency through the
> new 12Gb controller.

As I saw it supports something called "fastpath" (I must read something, I am a bit \
outdated in these matters) I imagined that it  might be a more efficient transfer \
method which, despite working at 6 Gbps, might explain a  gain in performance.

> By the way, if you run with INVARIANTS enabled, you may run into some
> issues (i.e. a panic) on reboot until we merge r265485 to stable/10.

I am running stable/10, and  I'm not running INVARIANTS. Anyway I will be tracking \
stable/10 closely, thank you!

Great to have LSI so seriously involved!



Borja.



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