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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/addressnode_name
— 64-bit node nameport_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 defaultdev_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. Thedev_loss_tmo
value can be changed via thescsi_transport_fc
module parameterdev_loss_tmo
, although the driver can override this timeout value.The maximumdev_loss_tmo
value is 600 seconds. Ifdev_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 untildev_loss_tmo
expires and the queue is unblocked.
- Host:
/sys/class/fc_host/hostH/
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