User Manual

Rev 2.2-1.0.1
Mellanox Technologies
59
4.1.2.5 Multiple Connections from Initiator InfiniBand Port to the Target
Some system configurations may need multiple SRP connections from the SRP Initiator to the
same SRP
Target: to the same Target IB port, or to different IB ports on the same Target HCA.
In case of a single Target IB port, i.e., SRP connections use the same path, the configuration is
enabled using a dif
ferent initiator_ext value for each SRP connection. The initiator_ext value is a
16-hexadecimal-digit value specified in the connection command.
Also in case of two physical connections (i.e., network paths) from a single initiator IB port to
two dif
ferent IB ports on the same Target HCA, there is need for a different initiator_ext value on
each path. The conventions is to use the Target port GUID as the initiator_ext value for the rele-
vant path.
If you use srp_daemon with -n flag, it automatically assigns initiator_ext values according to this
convention. For example:
id_ext=200500A0B81146A1,ioc_guid=0002c90200402bec,\
dgid=fe800000000000000002c90200402bed,pkey=ffff,\
service_id=200500a0b81146a1,initiator_ext=ed2b400002c90200
Notes:
1. It is recommended to use the -n flag for all srp_daemon invocations.
2. ibsrpdm does not have a corresponding option.
3. srp_daemon.sh always uses the -n option (whether invoked manually by the user, or automat-
ically at startup by setting SRP_DAEMON_ENABLE to yes).
4.1.2.6 High Availability (HA)
Overview
High Availability works using the Device-Mapper (DM) multipath and the SRP daemon. Each
initiator is connected to the same tar
get from several ports/HCAs. The DM multipath is responsi-
ble for joining together different paths to the same target and for fail-over between paths when
one of them goes of
fline. Multipath will be executed on newly joined SCSI devices.
Each initiator should execute several instances of the SRP daemon, one for each port. At startup,
each SRP daemon detects the SRP
Targets in the fabric and sends requests to the ib_srp module
to connect to each of them. These SRP daemons also detect targets that subsequently join the fab-
ric, and send the ib_srp module requests to connect to them as well.
Operation
When a path (from port1) to a target fails, the ib_srp module starts an error recovery process. If
this process gets to the reset_host stage and there is no path to the tar
get from this port, ib_srp
will remove this scsi_host. After the scsi_host is removed, multipath switches to another path to
this target (from another port/HCA).
When the failed path recovers, it will be detected by the SRP daemon. The SRP daemon will then
request ib_srp to connect to this tar
get. Once the connection is up, there will be a new scsi_host
for this target. Multipath will be executed on the devices of this host, returning to the original
state (prior to the failed path).