Time to increase MAXPHYS?

[Edward Tomasz Napierała]

On 0605T1849, Edward Tomasz Napierała wrote:
> 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.

Erm, this was obviously - or perhaps not - say: when testing cfumass(4).
As in, Windows and OSX both seem to issue 1MB requests to USB Mass Storage
devices.