LINUX REMOVING A STORAGE DEVICE

拼搏现实的明天。 2024-04-19 09:14 56阅读 0赞

## 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”][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”][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 `free` can also be used to display the total memory).
 *  Swapping is active (non-zero `si` and `so` columns in the `vmstat` output).

The general procedure for removing all access to a device is as follows:

**Procedure 1.1. Ensuring a Clean Device Removal**

1.  Close all users of the device and backup device data as needed.
2.  Use `umount` to unmount any file systems that mounted the device.
3.  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.
4.  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`.
5.  Run `blockdev –flushbufs device` to flush any outstanding I/O to all paths to the device. This is particularly important for raw devices, where there is no `umount` or `vgreduce` operation to cause an I/O flush.
6.  Remove any reference to the device's path-based name, like `/dev/sd`, `/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.
7.  Finally, remove each path to the device 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.
    
    Another variation of this operation is `echo 1 > /sys/class/scsi_device/h:c:t:l/device/delete`, where `h` is the HBA number, `c` is the channel on the HBA, `t` is the SCSI target ID, and `l` is the LUN.
    
    **Note**
    
    The 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 `lsscsi`, `scsi_id`, `multipath -l`, and `ls -l /dev/disk/by-*`.

After performing [Procedure 1.1, “Ensuring a Clean Device Removal”][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”][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”][Section 1.8_ _Scanning Storage Interconnects].

[Section 1.3.1_ _WWID]: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/online_storage_reconfiguration_guide/persistent_naming#persistent_naming-wwid
[Section 1.6_ _Adding a Storage Device or Path]: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/online_storage_reconfiguration_guide/adding_storage-device-or-path
[Procedure 1.1_ _Ensuring a Clean Device Removal]: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/online_storage_reconfiguration_guide/removing_devices#clean-device-removal
[Section 1.8_ _Scanning Storage Interconnects]: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/online_storage_reconfiguration_guide/scanning-storage-interconnects