User Manual

Rev 2.3-1.0.1
Mellanox Technologies
161
3.3 Storage Protocols
3.3.1 SCSI RDMA Protocol (SRP)
As described in Section 3.3.1, the SCSI RDMA Protocol (SRP) is designed to take full advantage
of the protocol off-load and RDMA features provided by the InfiniBand architecture. SRP allows
a lar
ge body of SCSI software to be readily used on InfiniBand architecture. The SRP Initiator
controls the connection to an SRP Target in order to provide access to remote storage devices
across an InfiniBand fabric. The kSRP Target resides in an IO unit and provides storage services.
Section 3.3.1.1 describes the SRP Initiator included in Mellanox OFED for Linux. This package,
however, does not include an SRP
Target.
3.3.1.1 SRP Initiator
This SRP Initiator is based on open source from OpenFabrics (www
.openfabrics.org) that imple-
ments the SCSI RDMA Protocol-2 (SRP-2). SRP-2 is described in Document # T10/1524-D
available from http://www
.t10.org.
The SRP Initiator supports
• Basic SCSI Primary Commands -3 (SPC-3)
(www.t10.org/ftp/t10/drafts/spc3/spc3r21b.pdf)
• Basic SCSI Block Commands -2 (SBC-2)
(www.t10.org/ftp/t10/drafts/sbc2/sbc2r16.pdf)
• Basic functionality, task management and limited error handling
Loading SRP Initiator
To load the SRP module, either execute the “
modprobe ib_srp” command after the OFED driver
is up, or change the value of SRP_LOAD in
/etc/infiniband/openib.conf to “yes”.
For the changes to take effect, run: /etc/init.d/openibd restart
When loading the ib_srp module, it is possible to set the module parameter
srp_sg_tablesize. This is the maximum number of gather/scatter entries per I/O
(default: 12).
3.3.1.1.1 SRP Module Parameters
When loading the SRP module, the following parameters can be set (viewable by the "modinfo
ib_srp"
command):
cmd_sg_entries Default number of gather/scatter entries in the SRP command (default is
12, max 255)
allow_ext_sg Default behavior when there are more than cmd_sg_entries S/G entries
after mapping; fails the request when false (default false)
topspin_workarounds Enable workarounds for Topspin/Cisco SRP target bugs