On 0604T0952, Hans Petter Selasky wrote:
> On 06/04/17 09:39, Tomoaki AOKI wrote:
> > Hi
> > 
> > One possibility would be to make it MD build-time OTIONS,
> > defaulting 1M on regular systems and 128k on smaller systems.
> > 
> > Of course I guess making it a tunable (or sysctl) would be best,
> > though.
> > 
> Hi,
> A tunable sysctl would be fine, but beware that commonly used firmware 
> out there produced in the millions might hang in a non-recoverable way 
> if you exceed their "internal limits". Conditionally lowering this 
> definition is fine, but increasing it needs to be carefully verified.
> For example many USB devices are only tested with OS'es like Windows and 
> MacOS and if these have any kind of limitation on the SCSI transfer 
> sizes, it is very likely many devices out there do not support any 
> larger transfer sizes either.

FWIW, when testing cfiscsi(4) with Windows and OSX I've noticed
that both issue 1MB requests.  I wouldn't be surprised if they avoided
doing that for older devices, depending on eg the SCSI version reported
by device.

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