3ware driver maximum request size

3ware driver maximum request size

[Steve Lord]

Does anyone know why the 3ware driver caps I/O at 128K bytes per scsi
request? The driver defines a scatter gather array which will always
cope with at least twice this.

I am running with the TW_MAX_SECTORS constant at 512 and getting
256K I/Os to a 6+1 raid5 lun on a 9550SX. By my calculations this
does not exceed the defined sizes of the scatter gather arrays for
this type of device (but would I guess for the escalade variant
in the code).

I know nothing about the hardware itself, but if this works it seems
like a worthwhile change for the newer devices.

Thanks

   Steve Lord

Re: 3ware driver maximum request size

[adam radford]

Steve,

It's capped at 128k per request because that is the max size the firmware
was tested with.  If you increase that number, it is at your own risk, and
you may have problems.

-Adam

On 8/17/06, Steve Lord <lord@xfs.org> wrote:
>
> Does anyone know why the 3ware driver caps I/O at 128K bytes per scsi
> request? The driver defines a scatter gather array which will always
> cope with at least twice this.
>
> I am running with the TW_MAX_SECTORS constant at 512 and getting
> 256K I/Os to a 6+1 raid5 lun on a 9550SX. By my calculations this
> does not exceed the defined sizes of the scatter gather arrays for
> this type of device (but would I guess for the escalade variant
> in the code).
>
> I know nothing about the hardware itself, but if this works it seems
> like a worthwhile change for the newer devices.
>
> Thanks
>
>    Steve Lord
>
>

Re: 3ware driver maximum request size

[Steve Lord]

adam radford wrote:
> Steve,
> 
> It's capped at 128k per request because that is the max size the firmware
> was tested with.  If you increase that number, it is at your own risk, and
> you may have problems.
> 
> -Adam
> 

Thanks Adam,

It does seem capable of handling it under basic testing, guess I will take that
under advisement. So far the perf difference is not that large, so maybe it is
best left alone.

Steve