I have a hard time in getting this. I am not getting how there are eight paths from the server to storage. Can anyone help me with a diagram of the connections from server-switch-storage.
1) Are these four HBA ports? I guess so.
[Dev][root@fdcc ~]# lsdev -Cc adapter |grep fcs*
fcs0 Available 11-T1 Virtual Fibre Channel Client Adapter
fcs1 Available 12-T1 Virtual Fibre Channel Client Adapter
fcs2 Available 13-T1 Virtual Fibre Channel Client Adapter
fcs3 Available 14-T1 Virtual Fibre Channel Client Adapter
2) No idea about below? Please explain about this.
[Dev][root@fdcc ~]# lspath
Enabled hdisk1 vscsi0
Enabled hdisk0 vscsi0
Enabled hdisk2 vscsi0
Enabled hdisk1 vscsi1
Enabled hdisk0 vscsi1
Enabled hdisk2 vscsi1
3) These are HBA ports. Right?
[Dev][root@fdcc ~]# powermt display hba_mode
Hitachi logical device count=74
==============================================================================
----- Host Bus Adapters --------- ------ I/O Paths ----- Stats
### HW Path Summary Total Dead Q-IOs Mode
==============================================================================
0 fscsi0 optimal 148 0 0 Enabled
1 fscsi1 optimal 148 0 0 Enabled
2 fscsi2 optimal 148 0 0 Enabled
3 fscsi3 optimal 148 0 0 Enabled
4) These are paths and I don't understand how fscsi0 goes to 3A and 3C. How can the port have two connections to two controllers. I have hard time in getting this.
[Dev][root@fdcc ~]# powermt display paths
Hitachi logical device count=74
==============================================================================
----- Host Bus Adapters --------- ------ Storage System ----- - I/O Paths -
### HW Path ID Interface Total Dead
==============================================================================
0 fscsi0 471399 3C 74 0
0 fscsi0 471399 3A 74 0
1 fscsi1 471399 4C 74 0
1 fscsi1 471399 4A 74 0
2 fscsi2 471399 3C 74 0
2 fscsi2 471399 3A 74 0
3 fscsi3 471399 4C 74 0
3 fscsi3 471399 4A 74 0
5) What is the Wt-Q column?
[Dev][root@fdcc ~]# powermt display port_mode
Storage class = Hitachi
==============================================================================
----------- Storage System --------------- -- I/O Paths -- --- Stats ---
ID Interface Wt_Q Total Dead Q-IOs Mode
==============================================================================
471399 4C 256 148 0 0 Enabled
471399 4A 256 148 0 0 Enabled
471399 3C 256 148 0 0 Enabled
471399 3A 256 148 0 0 Enabled
There are 8 paths to the LDEV, because you are dealing with Fibre-channel SAN, where FC traffic between HBA ports and Storage ports is routed through Fibre-channel switched fabrics. Best practices urge to use so-called Dual-Fabric configurations, therefore based on your outputs, I can suppose, HBAs fscsi0, fscsi2 along with ports 3A, 3C are connected to the first fabric, while fscsi1/fscsi3 and 4A/4C are in the second fabric.
Wt-Q looks for me like "Wait queue". For modern enterprise Hitachi storage arrays the recommended maximum number of SCSI commands is 2048 per FC-port, 32 per logical unit but you must consult the manual four your model.
A new picture, that represents physical possible Fabrics connection is attached:
Logical connections are depicted in the first pictue. The mechanism which rules connections on logical level is called "Zoning", and saying simple it can be somehow compared to VLANs in LAN switches. So you can specify which WWNs and/or ports are allowed to communicate.