Red Hat Enterprise Linux 8 Essentials Book now available.
Purchase a copy of Red Hat Enterprise Linux 8 (RHEL 8) Essentials in eBook ($24.99) or Print ($36.99) format
Red Hat Enterprise Linux 8 Essentials Print and eBook (ePub/PDF/Kindle) editions contain 31 chapters and over 250 pages
21.4. 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 21.3.1, “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 21.6, “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
free can also be used to display the total memory).
Swapping is active (non-zero
so columns in the
The general procedure for removing all access to a device is as follows:
Procedure 21.1. Ensuring a Clean Device Removal
Close all users of the device and backup device data as needed.
umount to unmount any file systems that mounted the device.
Remove the device from any
md and 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
pvmove command, then use the
vgreduce command to remove the physical volume, and (optionally)
pvremove to remove the LVM metadata from the disk.
If the device uses multipathing, run
multipath -l and note all the paths to the device. Afterwards, remove the multipathed device using
multipath -f device.
blockdev –flushbufs to flush any outstanding I/O to all paths to the device. This is particularly important for raw devices, where there is no
vgreduce operation to cause an I/O flush.
Remove any reference to the device's path-based name, like
/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.
Finally, remove each path to the device from the SCSI subsystem. To do so, use the command
echo 1 > /sys/block/ where
sde, for example.
Another variation of this operation is
echo 1 > /sys/class/scsi_device/, where
is the HBA number,
is the channel on the HBA,
is the SCSI target ID, and
is the LUN.
The older form of these commands,
echo "scsi remove-single-device 0 0 0 0" > /proc/scsi/scsi, is deprecated.
You can determine the
, 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-*.
Other procedures, such as the physical removal of the device, followed by a rescan of the SCSI bus (as described in Section 21.9, “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 21.9, “Scanning Storage Interconnects”