Fibre Channel; Fibre Channel Api - Red Hat ENTERPRISE LINUX 5.5 - ONLINE STORAGE GUIDE Manual

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2. 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.

2.1. 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.
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