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
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.
port_id— 24-bit port ID/address
node_name— 64-bit node name
port_name— 64-bit port name
- Remote Port:
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_tmovalue 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_tmovalue can be changed via the
dev_loss_tmo, although the driver can override this timeout value.The maximum
dev_loss_tmovalue is 600 seconds. If
dev_loss_tmois 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_tmoexpires and the queue is unblocked.
1.1.2. Native Fibre Channel Drivers and Capabilities
Red Hat Enterprise Linux 5 ships with the following native fibre channel drivers:
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