Removing A Path To A Storage Device; Adding A Storage Device Or Path - Red Hat ENTERPRISE LINUX 5.5 - ONLINE STORAGE GUIDE Manual

Online Storage Guide
Procedure 1, "Ensuring a Clean Device
After performing
removed safely from a running system. It is not necessary to stop I/O to other devices while doing so.
Other procedures, such as the physical removal of the device, followed by a rescan of the SCSI bus
Section 9, "Scanning Storage
(as described in
be updated to reflect the change, are not recommended. This will cause delays due to I/O timeouts,
and devices may be removed unexpectedly. If it is necessary to perform a rescan of an interconnect, it
must be done while I/O is paused, as described in

6. Removing a Path to a Storage Device

If you are removing a path to a device that uses multipathing (without affecting other paths to the
device), then the general procedure is as follows:
Procedure 2. Removing a Path to a Storage Device
1. Remove any reference to the device's path-based name, like /dev/sd or /dev/disk/by-path
or the major:minor number, in applications, scripts, or utilities on the system. This is important
in ensuring that different devices added in the future will not be mistaken for the current device.
2. Take the path offline using echo offline > /sys/block/sda/device/state.
This will cause any subsequent IO sent to the device on this path to be failed immediately.
Device-mapper-multipath will continue to use the remaining paths to the device.
3. Remove the path from the SCSI subsystem. To do so, use the command echo 1 > /sys/
block/device-name/device/delete where device-name may be sde, for example (as
Procedure 1, "Ensuring a Clean Device
described in
Procedure 2, "Removing a Path to a Storage
After performing
from the running system. It is not necessary to stop I/O while this is done, as device-mapper-
multipath will re-route I/O to remaining paths according to the configured path grouping and failover
policies.
Other procedures, such as the physical removal of the cable, followed by a rescan of the SCSI bus
to cause the operating system state to be updated to reflect the change, are not recommended. This
will cause delays due to I/O timeouts, and devices may be removed unexpectedly. If it is necessary to
perform a rescan of an interconnect, it must be done while I/O is paused, as described in
"Scanning Storage Interconnects".

7. Adding a Storage Device or Path

When adding a device, be aware that the path-based device name (/dev/sd name, major:minor
number, and /dev/disk/by-path name, for example) the system assigns to the new device may
have been previously in use by a device that has since been removed. As such, ensure that all old
references to the path-based device name have been removed. Otherwise, the new device may be
mistaken for the old device.
The first step in adding a storage device or path is to physically enable access to the new storage
device, or a new path to an existing device. This is done using vendor-specific commands at the Fibre
Channel or iSCSI storage server. When doing so, note the LUN value for the new storage that will be
presented to your host. If the storage server is Fibre Channel, also take note of the World Wide Node
Name (WWNN) of the storage server, and determine whether there is a single WWNN for all ports on
12
Removal", a device can be physically
Interconnects") to cause the operating system state to
Section 9, "Scanning Storage
Removal").
Device", the path can be safely removed
Interconnects".
Section 9,