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62 lines
3.3 KiB
Plaintext
62 lines
3.3 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 adding new devices to the devices file necessarily look outside
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the existing devices file to find the devices to add. pvcreate, vgcreate,
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and vgextend also look outside the devices file to create new PVs and add
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them 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.)
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These 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, lvm performs extra scanning to
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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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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 in \fI#DEFAULT_SYS_DIR#/devices\fP, which allows lvm
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to be used with different sets of devices, e.g. system devices do not need
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to be exposed to a specific application, and the application can use lvm on
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its own devices that are not exposed to the system. The option
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--devicesfile <filename> is used to select the devices file to use with the
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command. Without the option set, the default system devices file is used.
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Setting --devicesfile "" causes lvm to not use a devices file.
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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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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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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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