Bug 784405

The RHEL 6 Storage Administration Guide:

http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6-Beta/html-single/Storage_Administration_Guide/index.html

Chapter 24. Online Storage Management

Describes how to add or remove a device (or a path to a device)
while I/O is on-going. The manual indicates that this must be done one
device (or path) at a time. The following fully-specified commands must
be used:

to delete: echo 1 > /sys/class/scsi_device/h:c:t:l/device/delete

or

to add: echo "c t l" > /sys/class/scsi_host/hosth/scan

Later, in the section:
 
24.9. Scanning Storage Interconnects

The manual describes several ways to entirely re-scan one or more
storage interconnects while the system is running: 

1. echo "1" > /sys/class/fc_host/host/issue_lip
2. /usr/bin/rescan-scsi-bus.sh
3. echo "- - -" > /sys/class/scsi_host/hosth/scan
4. rmmod driver-name or modprobe driver-name

The manual stipulates that these commands can only be used when
1) All I/O on the interconnect is paused and flushed, and 
2) the system is not under memory pressure. 
These precautions are there to reduce the risk of any errors during
scanning, or delays, or the possible unexpected addition and removal of
multiple devices at the same time. 

The feedback we have gotten is that the requirement to fully-specify the
scan command is difficult and error prone. In response to this, we have
conducted some targeted code review and testing. We have determined that, as of RHEL 5.6, it is safe to allow wildcards in the search command, as follows:

echo "- - -" > /sys/class/scsi_host/hosth/scan

(This command scans all channels, targets and LUNs or a particular HBA
port.)

A change to reflect this new capability is needed on this manual, as well as the RHEL 5 Online Storage Reconfiguration Guide.