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When adding a device to the devices file with --adddev, lvm by default chooses the best device ID type for the new device. The new --deviceidtype option allows the user to override the built in preference. This is useful if there's a problem with the default type, or if a secondary type is preferrable. If the specified deviceidtype does not produce a device ID, then lvm falls back to the preference it would otherwise use.
102 lines
4.6 KiB
Plaintext
102 lines
4.6 KiB
Plaintext
The LVM devices file lists devices that lvm can use. The default file is
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\fI#DEFAULT_SYS_DIR#/devices/system.devices\fP, and the \fBlvmdevices\fP(8) command is used to
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add or remove device entries. If the file does not exist, or if lvm.conf
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includes use_devicesfile=0, then lvm will not use a devices file.
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.P
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To use a device with lvm, add it to the devices file with the command
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lvmdevices --adddev, and to prevent lvm from seeing or using a device,
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remove it from the devices file with lvmdevices --deldev. The
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vgimportdevices(8) command adds all PVs from a VG to the devices file,
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and updates the VG metadata to include device IDs of the PVs.
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.P
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Commands that add new devices to the devices file necessarily look outside
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the existing devices file to find the devices being added. pvcreate,
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vgcreate, and vgextend also look outside the devices file to create new
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PVs and add those PVs to the devices file.
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.P
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LVM records devices in the devices file using hardware-specific IDs, such
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as the WWID, and attempts to use subsystem-specific IDs for virtual device
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types (which also aim to be as unique and stable as possible.) These
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device IDs are also written in the VG metadata. When no hardware or
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virtual ID is available, lvm falls back using the unstable device name as
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the device ID. When devnames are used as IDs, lvm performs extra scanning
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to find devices if their devname changes, e.g. after reboot.
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.P
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When proper device IDs are used, an lvm command will not look at devices
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outside the devices file, but when devnames are used as a fallback, lvm
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will scan devices outside the devices file to locate PVs on renamed
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devices. A config setting search_for_devnames can be used to control the
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scanning for renamed devname entries.
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.P
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Related to the devices file, the new command option --devices <devnames>
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allows a list of devices to be specified for the command to use,
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overriding the devices file. The listed devices act as a sort of devices
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file in terms of limiting which devices lvm will see and use. Devices
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that are not listed will appear to be missing to the lvm command.
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.P
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Multiple devices files can be kept \fI#DEFAULT_SYS_DIR#/devices\fP, which
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allows lvm to be used with different sets of devices. For example, system
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devices do not need to be exposed to a specific application, and the
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application can use lvm on its own devices that are not exposed to the
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system. The option --devicesfile <filename> is used to select the devices
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file to use with the command. Without the option set, the default system
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devices file is used.
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.P
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Setting --devicesfile "" causes lvm to not use a devices file.
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.P
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With no devices file, lvm will use any device on the system, and applies
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the filter to limit the full set of system devices. With a devices file,
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the regex filter is not used, and the filter settings in lvm.conf or the
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command line are ignored. The vgimportdevices command is one exception
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which does apply the regex filter when looking for a VG to import.
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.P
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If a devices file exists, lvm will use it, even if it's empty. An empty
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devices file means lvm will see no devices.
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If the system devices file does not yet exist, the pvcreate or vgcreate
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commands will create it if they see no existing VGs on the system.
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lvmdevices --addev and vgimportdevices will always create a new devices file
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if it does not yet exist.
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.P
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It is recommended to use lvm commands to make changes to the devices file to
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ensure proper updates.
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.P
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The device ID and device ID type are included in the VG metadata and can
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be reported with pvs -o deviceid,deviceidtype. (Note that the lvmdevices
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command does not update VG metadata, but subsequent lvm commands modifying
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the metadata will include the device ID.)
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.P
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Possible device ID types are:
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.br
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.IP \[bu] 2
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.B sys_wwid
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uses the wwid reported by sysfs. This is the first choice for non-virtual
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devices.
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.IP \[bu] 2
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.B sys_serial
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uses the serial number reported by sysfs. This is the second choice for
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non-virtual devices.
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.IP \[bu] 2
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.B mpath_uuid
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is used for dm multipath devices, reported by sysfs.
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.IP \[bu] 2
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.B crypt_uuid
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is used for dm crypt devices, reported by sysfs.
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.IP \[bu] 2
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.B md_uuid
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is used for md devices, reported by sysfs.
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.B lvmlv_uuid
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is used if a PV is placed on top of an lvm LV, reported by sysfs.
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.IP \[bu] 2
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.B loop_file
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is used for loop devices, the backing file name repored by sysfs.
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.IP \[bu] 2
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.B devname
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the device name is used if no other type applies.
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.P
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The default choice for device ID type can be overriden using lvmdevices
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--addev --deviceidtype <type>. If the specified type is available for the
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device it will be used, otherwise the device will be added using the type
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that would otherwise be chosen.
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