Chapter 1. Online Storage Reconfiguration

1.1. Fibre Channel

This section discusses the Fibre Channel API, native Red Hat Enterprise Linux 5 Fibre Channel drivers, and the Fibre Channel capabilities of these drivers.

1.1.1. Fibre Channel API

Below is a list of /sys/class/ directories that contain files used to provide the userspace API. In each item, host numbers are designated by H, bus numbers are B, targets are T, logical unit numbers (LUNs) are L, and remote port numbers are R.

Important

If your system is using multipath software, Red Hat recommends that you consult your hardware vendor before changing any of the values described in this section.
Transport: /sys/class/fc_transport/targetH:B:T/
  • port_id — 24-bit port ID/address
  • node_name — 64-bit node name
  • port_name — 64-bit port name
Remote Port: /sys/class/fc_remote_ports/rport-H:B-R/
  • port_id
  • node_name
  • port_name
  • dev_loss_tmo — number of seconds to wait before marking a link as "bad". Once a link is marked bad, IO running on its corresponding path (along with any new IO on that path) will be failed.
    The default dev_loss_tmo value varies, depending on which driver/device is used. If a Qlogic adapter is used, the default is 35 seconds, while if an Emulex adapter is used, it is 30 seconds. The dev_loss_tmo value can be changed via the scsi_transport_fc module parameter dev_loss_tmo, although the driver can override this timeout value.
    The maximum dev_loss_tmo value is 600 seconds. If dev_loss_tmo is set to zero or any value greater than 600, the driver's internal timeouts will be used instead.
  • fast_io_fail_tmo — length of time to wait before failing IO executed when a link problem is detected. IO that reaches the driver will fail. If IO is in a blocked queue, it will not be failed until dev_loss_tmo expires and the queue is unblocked.
Host: /sys/class/fc_host/hostH/
  • port_id
  • issue_lip — instructs the driver to rediscover remote ports.

1.1.2. Native Fibre Channel Drivers and Capabilities

Red Hat Enterprise Linux 5 ships with the following native fibre channel drivers:
  • lpfc
  • qla2xxx
  • zfcp
  • mptfc
Table 1.1, “Fibre-Channel API Capabilities” describes the different fibre-channel API capabilities of each native Red Hat Enterprise Linux 5 driver. X denotes support for the capability.

Table 1.1. Fibre-Channel API Capabilities

lpfc qla2xxx zfcp mptfc
Transport port_id X X X X
Transport node_name X X X X
Transport port_name X X X X
Remote Port dev_loss_tmo X X X X
Remote Port fast_io_fail_tmo X X [a]
Host port_id X X X X
Host issue_lip X X
[a] Supported as of Red Hat Enterprise Linux 5.4