Red Hat Training
A Red Hat training course is available for Red Hat Enterprise Linux
1.4. Removing a Storage Device
Before removing access to the storage device itself, it is advisable to back up data from the device first. Afterwards, flush I/O and remove all operating system references to the device (as described below). If the device uses multipathing, then do this for the multipath "pseudo device" (Section 1.3.1, “WWID”) and each of the identifiers that represent a path to the device. If you are only removing a path to a multipath device, and other paths will remain, then the procedure is simpler, as described in Section 1.6, “Adding a Storage Device or Path”.
Removal of a storage device is not recommended when the system is under memory pressure, since the I/O flush will add to the load. To determine the level of memory pressure, run the command
vmstat 1 100; device removal is not recommended if:
- Free memory is less than 5% of the total memory in more than 10 samples per 100 (the command
freecan also be used to display the total memory).
- Swapping is active (non-zero
socolumns in the
The general procedure for removing all access to a device is as follows:
Procedure 1.1. Ensuring a Clean Device Removal
- Close all users of the device and backup device data as needed.
umountto unmount any file systems that mounted the device.
- Remove the device from any
mdand LVM volume using it. If the device is a member of an LVM Volume group, then it may be necessary to move data off the device using the
pvmovecommand, then use the
vgreducecommand to remove the physical volume, and (optionally)
pvremoveto remove the LVM metadata from the disk.
- If the device uses multipathing, run
multipath -land note all the paths to the device. Afterwards, remove the multipathed device using
multipath -f device.
blockdev –flushbufs deviceto flush any outstanding I/O to all paths to the device. This is particularly important for raw devices, where there is no
vgreduceoperation to cause an I/O flush.
- Remove any reference to the device's path-based name, like
major:minornumber, 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.
- Finally, remove each path to the device from the SCSI subsystem. To do so, use the command
echo 1 > /sys/block/device-name/device/deletewhere
sde, for example.Another variation of this operation is
echo 1 > /sys/class/scsi_device/h:c:t:l/device/delete, where
his the HBA number,
cis the channel on the HBA,
tis the SCSI target ID, and
lis the LUN.
NoteThe older form of these commands,
echo "scsi remove-single-device 0 0 0 0" > /proc/scsi/scsi, is deprecated.
You can determine the
device-name, HBA number, HBA channel, SCSI target ID and LUN for a device from various commands, such as
multipath -l, and
ls -l /dev/disk/by-*.
After performing Procedure 1.1, “Ensuring a Clean Device Removal”, a device can be physically 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 (as described in Section 1.8, “Scanning Storage Interconnects”) 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 Section 1.8, “Scanning Storage Interconnects”.