Re: USB Mass Storage: command size limits
Re: USB Mass Storage: command size limits
- Subject: Re: USB Mass Storage: command size limits
- From: Chris Sarcone <email@hidden>
- Date: Thu, 26 Jun 2008 09:31:37 -0700
Andy --Why does the mac never send commands larger than 128kB to a USB mass
storage device?
By default, most USB storage devices have issues due to Windows not sending large I/Os.
You should check the IOUSBMassStorageClass code which allows you to specify keys in the SCSI Device Charateristics dictionary including max block count or max byte count (i.e. you don't have to write any code to do this). I was wondering if I could tweak this for our USB device, which can
support bigger commands. However it looks like the traffic is limited by
IOBlockStorageDriver.
Yes, you can and should. How could I change the behaviour of IOBlockStorageDriver? I can subclass
and instantiate IOBlockStorageServices from a custom LUN driver, but how
could I cause a subclass of IOBlockStorageDriver to be loaded for my
device?
Refer to the IOUSBMassStorageClass and you can look at information in AppleStorageDrivers plugins that shows how some device overrides enable different I/O sizes...
HTH,
-- Chris
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