Re: Maximum data size in a single transfer for MS driver

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On Wed, 2010-02-17 at 18:07 +0530, Ramya Desai wrote:
> What is  the number of maximum sectors that SCSI can send to MS driver
> in a single data transfer?

I have no idea what the MS driver is, so it's impossible to answer
specifically.  Generically, for drivers that expect a contiguous sg
list, then 128 elements (512k) is the maximum.  For drivers updated to
use the sg chaining API (which is at least all of those in
drivers/scsi), there is no maximum except what the hardware is limited
to.

> I changed the max_sectors in struct scsi_host_template
> usb_stor_host_template structure to 2048. Still, SCSI is sending 1024
> sectors (512 KB) in a single data transfer.
> I know that my device supports 1 MB data in a sigle transfer.  How can
> I change this to 1 MB?

As long as the driver supports chaining, you increase it
in /sys/block/dev>/queue/max_sectors_kb.  For compatibility reasons this
stays clamped at 512 unless a user specifically raises it.

James


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