System information

Chapter 25. Online Storage Management
It is often desirable to add, remove or re-size storage devices while the operating system is running,
and without rebooting. This chapter outlines the procedures that may be used to reconfigure storage
devices on Red Hat Enterprise Linux 6 host systems while the system is running. It covers iSCSI and
Fibre Channel storage interconnects; other interconnect types may be added it the future.
This chapter focuses on adding, removing, modifying, and monitoring storage devices. It does not
discuss the Fibre Channel or iSCSI protocols in detail. For more information about these protocols,
refer to other documentation.
This chapter makes reference to various sysfs objects. Red Hat advises that the sysfs object
names and directory structure are subject to change in major Red Hat Enterprise Linux releases. This
is because the upstream Linux kernel does not provide a stable internal API. For guidelines on how
to reference sysfs objects in a transportable way, refer to the document
/usr/share/d o c/kernel -d o c-version/D o cumentati o n/sysfs-rul es. txt in the kernel
source tree for guidelines.
Warning
Online storage reconfiguration must be done carefully. System failures or interruptions during
the process can lead to unexpected results. Red Hat advises that you reduce system load to
the maximum extent possible during the change operations. This will reduce the chance of I/O
errors, out-of-memory errors, or similar errors occurring in the midst of a configuration change.
The following sections provide more specific guidelines regarding this.
In addition, Red Hat recommends that you back up all data before reconfiguring online
storage.
25.1. Fibre Channel
This section discusses the Fibre Channel API, native Red Hat Enterprise Linux 6 Fibre Channel
drivers, and the Fibre Channel capabilities of these drivers.
25.1.1. Fibre Channel API
Below is a list of /sys/cl ass/ 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.
T ran sport : /sys/cl ass/fc_transpo rt/targ etH: B: T/
po rt_i d — 24-bit port ID/address
no d e_name — 64-bit node name
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