pSeries VIO Server Tuning
Server FCS Adapter Settings
| Option | Default | Meaning | Options | Comments |
| lg_term_dma | 0x800000 | Controls DMA memory area for control IO buffers. |
0x100000 0x200000 0x400000 0x800000 0x1000000 0x2000000 0x4000000 0x8000000 |
The size, in bytes, of the pool needed to map control
structures and long term mapped buffers. The default value of 0x800000 is typically sufficient
for I/O. You can increase the size if a large number of FCP (Fiber Channel Protocol) targets
are attached. 0x100000 = 1 MB 0x200000 = 2 MB 0x400000 = 4 MB 0x800000 = 8 MB 0x1000000 = 16 MB 0x2000000 = 32 MB 0x4000000 = 64 MB 0x8000000 = 128 MB |
| max_xfer_size | 0x100000 | The maximum transfer size of I/O requests. |
0x100000 0x200000 0x400000 0x800000 0x1000000 |
Indicates the maximum transfer size (in bytes) of
requests. The default value is typically sufficient for all disk activity. Some tape applications
may require a larger value. The default value is 16 MB and all other allowable values set
the DMA area to 128 MB. 0x100000 = 16 MB 0x200000 = 128 MB 0x400000 = 128 MB 0x800000 = 128 MB 0x1000000 = 128 MB |
| num_cmd_elems | 200 | Number of concurrent commands the adapter can queue. | 0 to 2048 | Indicates the maximum number of commands that can be
outstanding at the FC adapter. It may need to be changed if the devices attached to the adapter
can accept more comands. Recommended settings of 2000 for most disk arrays. |
Server FSCSI Adapter Settings
| Option | Default | Meaning | Options | Comments |
| dyntrk | no | Dynamic Tracking of Fibre Channel Devices | yes no |
Allows dynamic SAN changes to be implemented. When dynamic tracking of FC Devices is enabled, the FC adapter driver can detect when the Fiber Channel N_Port ID of a device changes and re-route traffic destined for that device to the new address while the devices are still online. Examples of events that can cause an N_Port ID to change are moving a cable between a switch and storage device from one switch port to another, connecting two separate switches via an Inter-Switch Link (ISL), and possibly rebooting a switch. |
| fc_err_recov | delayed_fail | FC Fabric Event Error RECOVERY Policy. | delayed_fail fast_fail |
Set FC fabric event error recovery fast_fail to yes if the
switches support it. Fast fail: If the driver receives a Registered State Change Notification (RSCN) from the switch, this could indicate a link loss between a remote storage port and switch. After an initial 15 second delay, the FC drivers will query to see if the device is on the fabric. If not, I/Os will be flushed back by the adapter. Future retries or new I/Os will fail immediately if the device is still not on the fabric. The storage driver should not delay between retries. Delayed fail: If dynamic tracking is set to 'yes' and the driver receives a Registered State Change Notification (RSCN) from the switch, this could indicate a link loss between a remote storage port and switch. After an initial 15 second delay, the FC drivers will query to see if the device is on the fabric. If not, I/Os will be flushed back by the adapter. Future retries or new I/Os will fail immediately if the device is still not on the fabric, although the storage driver drivers may inject a small delay (2-5 seconds) between I/O retries. If the FC drivers detects the device is on the fabric but the SCSI ID has changed, the FC device drivers will reroute traffic to the new SCSI ID. If dynamic tracking is set to "no" and an RSCN for a remote device is received, the FC drivers will not recover if the SCSI ID of a device changes, and I/Os will take longer to fail when a link loss occurs between a remote storage port and switch. This situation only occurs on machines running earlier versions of AIX. However, this may be desirable in single-path situations if dynamic tracking support is not a requirement. |
Examples - Changing Server Adapter Settings
| chdev -dev fcs0 -attr num_cmd_elems=2000 -perm | Will work but a reboot is required. |
| chdev -dev fcs0 -attr max_xfer_size=0x200000 -perm | Will work but a reboot is required. |
| chdev -dev fscsi0 -attr dyntrk=yes -perm | Will work but a reboot is required. |
| chdev -dev fscsi0 -attr fc_err_recov=fast_fail -perm | Will work but a reboot is required. |
|
chdev -dev fcs0 -attr num_cmd_elems=2000 -perm chdev -dev fcs0 -attr max_xfer_size=0x200000 -perm chdev -dev fscsi0 -attr dyntrk=yes -perm chdev -dev fscsi0 -attr fc_err_recov=fast_fail -perm rmdev -dev fcs0 -ucfg -recursive cfgdev Now repeate these steps for fcs1 and fscsi1. |
Overview of the steps required to make the adapter changes in a dual adapter configuration without the need to reboot the vio server. |