Virtual SAN 8 and iSCSI MaxTransferLength

[perdrix]

Hmmm MaxSGList is already set to 0x41 (65) which in a 64k system should allow 256kB buffers.

It would appear that Windows is applying an artificial 64kB limit.

I'll dig to try to find how to override this.

I looked at the device driver setting in Windows Device Manger. The driver is hplto.sys and the maximum buffer size is set to 16MB not 64kB.
I've opened a thread on HP's support forums to see what they have to say ...

What IOCTL are you using to get that MaxTransferLenght value?

Dave

[Michael (staff)]

We use IOCTL_STORAGE_QUERY_PROPERTY with PropertyId = StorageAdapterProperty to query the MaxTransferLength of devices.

[perdrix]

It would appear that this may be a limitation with the Adaptec Ultra320 drivers using the Windows x64 Storport interface.

http://ask.adaptec.com/app/answers/deta ... windows%3F says:

Attention: Newer 64-bit versions of Windows ignore the MaximumSGList parameter because the Storport driver architecture does not support this parameter. If you are using Windows Server 2003 x64, Windows 7 x64 or Windows Server 2008 (R2) x64 then only Storport drivers are supported and therefore the block size cannot be changed. It will always be the default value of 64k. All 32-bit Windows versions are using SCSIport drivers by default and with SCSIport the MaximumSGList parameter can be changed.

I believe from what I've read that it is possible to work round this limitation when using Storport drivers, but that the Adaptec U320 drivers didn't do so.

Thanks for all your help
Dave

[Michael (staff)]

Thank you, Dave!

[perdrix]

The annoying this is that if Microsemi were prepared to release the code, I could fix it in a very short time as I now know exactly what needs changing

Sadly their attitude is that these cards are "EOL" and they don't care to assist in any way.

Ho hum
Dave

[Michael (staff)]

Of course, it would be great to have it resolved.
Anyway, keep us updated if you will find the solution.