This entry is similar in theme to one of my previous posts about verifying your hdisk queue_depth settings with kdb. This time we want to check if an attribute for a Virtual FC (VFC) adapter has been modified and whether or not AIX has been restarted since the change. The attribute Im interested in is num_cmd_elems. This value is often changed from its default settings, in AIX environments, to improve I/O performance on SAN attached storage.

From kdb you can identify the VFC adapters configured on an AIX system using the vfcs subcommand. Not only does this tell you what adapters you have, but it also identifies the VIOS each adapter is connected to and the corresponding vfchost adapter. Nice!

(0)> vfcs

NAME ADDRESS STATE HOST HOST_ADAP OPENED NUM_ACTIVE

fcs0 0xF1000A00103D4000 0x0008 vio1 vfchost10 0x01 0x0000

fcs1 0xF1000A00103D6000 0x0008 vio2 vfchost10 0x01 0x0000

You can view the current (running) configuration of a VFC adapter using the kdb vfcs subcommand and the name of the VFC adapter, for example fcs1:

(0)> vfcs fcs1

adapter: fcs0 partition_num: 0x14 partition_name: aixlpar1

num_cmd_elems: 0xC8 location_code: U9119.FHA.87654A1-V20-C10-T1

state: 0x8 opened: 0x1 flags: 0x1

host_name: vio1 host_device: vfchost10

maxCmds: FA maxDMALength: 100000 SCSIid: 6F1E9A

portName: C050760399100168 nodeName: C050760399100168 nport_id:

6F1E9A

cmd_q.base_addr: 0xF1000A00102D0000 asyncq.base_addr: 0xF1000A0019761000

crq[0]: 0x8001000000000000 crq[1]: 0x8013960

ctl_head: 0x0 ctl_tail: 0x0

cmd_head: 0x0 cmd_tail: 0x0

pool_head: 0xF1000A001975BD08 pool_tail: 0xF1000A0019759D88

head_active: 0x0 tail_active: 0x0

cancel_head: 0xF1000A0019758090 cancel_tail: 0xF1000A0019758E58

num_cmds_allowed: 0xFA num_cmds_active: 0x0 num_cmds_pending: 0x0

head_flush_q: 0x0 tail_flush_q: 0x0 cmd_flush_q: 0x0

no_elem: 0x0 no_dma: 0x0 no_sglist: 0x0 bad_mad: 0x0 qfull: 0x0

h_dropped: 0x0 link_down_cnt: 0x0 num_frames: 0x0 tx_lock: 0x0

rcv_lock: 0x0 ctl_lock: 0x0 lock: 0xFFFFFFFFFFFFFFFF

ctl_event: 0xFFFFFFFFFFFFFFFF open_event: 0xFFFFFFFFFFFFFFFF

reset_cmd: 0x0 log_cmd: 0x0

link_cmd: 0x0 ctl_cmd->cmd_state: 0x0

inp_reqs: 0x12594 out_reqs: 0x1A7FD4 ctrl_reqs: 0x44

inp_bytes: 0x14973F90 out_bytes: 0xEC14EC18 npiv_logout_sent: 0x0

npiv_logout_rcvd: 0x0 act_hi_water: 0x10 pend_hi_water: 0x1

Using the output from this command we can determine the current (running) value for a number of VFC attributes, including num_cmd_elems.

So I start with an adapter with a num_cmd_elems value of 200. Both the lsattr command and kdb report 200 (C8 in hex) for num_cmd_elems.

# lsattr -El fcs1 -a num_cmd_elems

num_cmd_elems 200 Maximum Number of COMMAND Elements True

# echo vfcs fcs1 | kdb | grep num_cmd_elems

num_cmd_elems: 0xC8 location_code: U9119.FHA.87654A1-V20-C10-T1

I change num_cmd_elems to 400 with chdev P (remember, the P flag only updates the AIX ODM, and not the running configuration of the device in the AIX kernel. You must either reboot for this change to take effect or offline & online the device).

# chdev -l fcs1 -a num_cmd_elems=400 -P

fcs1 changed

Now the lsattr command reports num_cmd_elems is set to 400 in the ODM.

# lsattr -El fcs1 -a num_cmd_elems

num_cmd_elems 400 Maximum Number of COMMAND Elements True

But kdb still has num_cmd_elems set to C8 (200).