Issue with ppc64/vibmscsi

[Ivan Warren]

Folks,

It seems (by my experience) that the pSeries AIX based Virtual I/O Server
(at release 1.1.1.20) has a limit of 128K (256 sectors) request size when
performing I/Os over the Virtual SCSI interface (using the SRP/RDMA
hypervisor based transport).

The symptom is that some large I/Os will fail the adapter (putting it
offline).

The Virtual I/O server indicates an errlog entry of type "37DDE80C"
(Misbehaved Virtual SCSI Client)

I couldn't find any documentation on any fixed request size limit anywhere.

I attempted this, and this circumvents the problem (in my particular case) :

Set max_sectors=256 to the scsi_host_template in ibmvscsi.c

Of course, this is a bit .. brutal .. (it would limit the transfer size in
environments that probably do not need it, such as when talking to an
iSeries OS/400 or i5/OS partition) - And eventually, the limit in VIOS may
go away (if, as I suspect, this is an actual problem in the current VIOS
code).

So a config statement may be appropriate.. Or maybe just wait for a new VIOS
release or set pf PTFs..

--Ivan