lvmsystemid(7)



LVMSYSTEMID(7)                                                  LVMSYSTEMID(7)

NAME
       lvmsystemid -- LVM system ID

DESCRIPTION
       The  lvm(8)  system  ID restricts Volume Group (VG) access to one host.
       This is useful when a VG is placed on shared storage devices,  or  when
       local devices are visible to both host and guest operating systems.  In
       cases like these, a VG can be visible to multiple hosts  at  once,  and
       some mechanism is needed to protect it from being used by more than one
       host at a time.

       A VG's system ID identifies one host as the VG owner.  The host with  a
       matching system ID can use the VG and its LVs, while LVM on other hosts
       will ignore it.  This protects the VG from being accidentally used from
       other hosts.

       The  system  ID is a string that uniquely identifies a host.  It can be
       configured as a custom value, or it can be  assigned  automatically  by
       LVM  using  some  unique identifier already available on the host, e.g.
       machine-id or uname.

       When a new VG is created, the system ID of the local host  is  recorded
       in the VG metadata.  The creating host then owns the new VG, and LVM on
       other hosts will ignore it.  When an existing, exported VG is  imported
       (vgimport),  the  system  ID of the local host is saved in the VG meta-
       data, and the importing host owns the VG.

       A VG without a system ID can be used by LVM on any host where the  VG's
       devices  are  visible.   When  system  IDs are not used, device filters
       should be configured on all hosts to exclude the VG's devices from  all
       but one host.

       A  foreign VG is a VG seen by a host with an unmatching system ID, i.e.
       the system ID in the VG metadata does not match the system  ID  config-
       ured  on  the host.  If the host has no system ID, and the VG does, the
       VG is foreign and LVM will ignore it.  If the VG has no system ID,  ac-
       cess  is unrestricted, and LVM can access it from any host, whether the
       host has a system ID or not.

       Changes to a host's system ID and a VG's system ID can be made in  lim-
       ited  circumstances  (see vgexport and vgimport).  Improper changes can
       result in a host losing access to its VG, or a  VG  being  accidentally
       damaged by access from an unintended host.  Even limited changes to the
       VG system ID may not be perfectly reflected across hosts.  A  more  co-
       herent  view of shared storage requires an inter-host locking system to
       coordinate access.

       Valid system ID characters are the same as valid  VG  name  characters.
       If  a system ID contains invalid characters, those characters are omit-
       ted and remaining characters are used.  If a system ID is  longer  than
       the  maximum  name  length, the characters up to the maximum length are
       used.  The maximum length of a system ID is 128 characters.

       Print the system ID of a VG to check if it is set:

       vgs -o systemid VG

       Print the system ID of the local host to check if it is configured:

       lvm systemid

   Limitations and warnings
       To benefit fully from system ID, all hosts should have a system ID con-
       figured,  and  all VGs should have a system ID set.  Without any method
       to restrict access, e.g. system ID or device filters, a VG that is vis-
       ible to multiple hosts can be accidentally damaged or destroyed.

       o A  VG  without  a  system ID can be used without restriction from any
         host where it is visible, even from hosts that have a system ID.

       o Many VGs will not have a system ID set because LVM has not enabled it
         by  default,  and even when enabled, many VGs were created before the
         feature was added to LVM or enabled.  A system ID can be assigned  to
         these VGs by using vgchange --systemid (see below).

       o Two  hosts  should  not be assigned the same system ID.  Doing so de-
         feats the purpose of distinguishing different hosts with this value.

       o Orphan PVs (or unused devices) on shared storage are  unprotected  by
         the system ID feature.  Commands that use these PVs, such as vgcreate
         or vgextend, are not prevented from performing conflicting operations
         and  corrupting  the  PVs.  See the orphans section for more informa-
         tion.

       o The system ID does not protect devices in a VG  from  programs  other
         than LVM.

       o A  host using an old LVM version (without the system ID feature) will
         not recognize a system ID set in VGs.  The old LVM can read a VG with
         a  system  ID,  but is prevented from writing to the VG (or its LVs).
         The system ID feature changes the write mode of a VG, making  it  ap-
         pear read-only to previous versions of LVM.

         This  also means that if a host downgrades to the old LVM version, it
         would lose access to any VGs it had created with  a  system  ID.   To
         avoid  this,  the  system  ID should be removed from local VGs before
         downgrading LVM to a version without the system ID feature.

   Types of VG access
       A local VG is meant to be used by a single host.

       A shared or clustered VG is meant to be used by multiple hosts.

       These can be further distinguished as:

       Unrestricted: A local VG that has no system ID.  This VG type is unpro-
       tected and accessible to any host.

       Owned:  A  local  VG  that has a system ID set, as viewed from the host
       with a matching system ID (the owner).  This VG type  is  acessible  to
       the host.

       Foreign:  A  local VG that has a system ID set, as viewed from any host
       with an unmatching system ID (or no system ID).  It is owned by another
       host.  This VG type is not accessible to the host.

       Exported:  A  local  VG that has been exported with vgexport and has no
       system ID.  This VG type can only be accessed by  vgimport  which  will
       change it to owned.

       Shared:  A shared or "lockd" VG has the lock_type set and has no system
       ID.  A shared VG is meant to be used on shared  storage  from  multiple
       hosts,  and is only accessible to hosts using lvmlockd. Applicable only
       if LVM is compiled with lvmlockd support.

       Clustered: A clustered or "clvm" VG has the clustered flag set and  has
       no  system  ID.   A  clustered VG is meant to be used on shared storage
       from multiple hosts, and is only accessible to hosts using  clvmd.  Ap-
       plicable only if LVM is compiled with clvm support.

   Host system ID configuration
       A  host's  own  system ID can be defined in a number of ways.  lvm.conf
       global/system_id_source defines the method LVM will use to find the lo-
       cal system ID:

       none

              LVM  will  not  use  a  system ID.  LVM is allowed to access VGs
              without a system ID, and will create new VGs  without  a  system
              ID.  An undefined system_id_source is equivalent to none.

              lvm.conf
              global {
                  system_id_source = "none"
              }

       machineid

              The  content  of  /etc/machine-id  is  used  as the system ID if
              available.  See machine-id(5) and systemd-machine-id-setup(1) to
              check if machine-id is available on the host.

              lvm.conf
              global {
                  system_id_source = "machineid"
              }

       uname

              The  string utsname.nodename from uname(2) is used as the system
              ID.  A uname beginning with "localhost" is ignored  and  equiva-
              lent to none.

              lvm.conf
              global {
                  system_id_source = "uname"
              }

       lvmlocal

              The system ID is defined in lvmlocal.conf local/system_id.

              lvm.conf
              global {
                  system_id_source = "lvmlocal"
              }

              lvmlocal.conf
              local {
                  system_id = "example_name"
              }

       file

              The  system  ID  is  defined  in  a  file  specified by lvm.conf
              global/system_id_file.

              lvm.conf
              global {
                  system_id_source = "file"
                  system_id_file = "/path/to/file"
              }

       Changing system_id_source will likely cause the system ID of  the  host
       to  change,  which  will prevent the host from using VGs that it previ-
       ously used (see extra_system_ids below to handle this.)

       If a system_id_source other than none fails  to  produce  a  system  ID
       value,  it  is the equivalent of having none.  The host will be allowed
       to access VGs with no system ID, but will not be allowed to access  VGs
       with a system ID set.

   Overriding system ID
       In  some  cases, it may be necessary for a host to access VGs with dif-
       ferent system IDs, e.g. if a host's system ID changes, and it wants  to
       use VGs that it created with its old system ID.  To allow a host to ac-
       cess VGs with other system IDs, those other system IDs can be listed in
       lvmlocal.conf local/extra_system_ids.

       lvmlocal.conf
       local {
           extra_system_ids = [ "my_other_name" ]
       }

       A  safer  option  may  be configuring the extra values as needed on the
       command line as:
       --config 'local/extra_system_ids=["id"]'

   vgcreate
       In vgcreate, the host running the command assigns its own system ID  to
       the new VG.  To override this and set another system ID:

       vgcreate --systemid SystemID VG PVs

       Overriding  the host's system ID makes it possible for a host to create
       a VG that it may not be able to use.  Another host  with  a  system  ID
       matching  the  one specified may not recognize the new VG without manu-
       ally rescanning devices.

       If the --systemid argument is an empty string (""), the VG  is  created
       with  no  system  ID, making it accessible to other hosts (see warnings
       above.)

   report/display
       The system ID of a VG is displayed with the  "systemid"  reporting  op-
       tion.

       Report/display  commands ignore foreign VGs by default.  To report for-
       eign VGs, the --foreign option can be used.  This causes the VGs to  be
       read from disk.

       vgs --foreign -o +systemid

       When  a host with no system ID sees foreign VGs, it warns about them as
       they are skipped.  The host should be assigned a system ID, after which
       standard reporting commands will silently ignore foreign VGs.

   vgexport/vgimport
       vgexport clears the VG system ID when exporting the VG.

       vgimport  sets  the VG system ID to the system ID of the host doing the
       import.

   vgchange
       A host can change the system ID of its own VGs,  but  the  command  re-
       quires  confirmation  because  the host may lose access to the VG being
       changed:

       vgchange --systemid SystemID VG

       The system ID can be removed from a VG by specifying  an  empty  string
       ("") as the new system ID.  This makes the VG accessible to other hosts
       (see warnings above.)

       A host cannot directly change the system ID of a foreign VG.

       To move a VG from one host to another, vgexport and vgimport should  be
       used.

       To  forcibly gain ownership of a foreign VG, a host can temporarily add
       the foreign system ID to its extra_system_ids list, and change the sys-
       tem ID of the foreign VG to its own.  See Overriding system ID above.

   shared VGs
       A shared VG has no system ID set, allowing multiple hosts to use it via
       lvmlockd.  Changing a VG to shared will clear the existing  system  ID.
       Applicable only if LVM is compiled with lvmlockd support.

   clustered VGs
       A  clustered/clvm  VG  has no system ID set, allowing multiple hosts to
       use it via clvmd.  Changing a VG to clustered will clear  the  existing
       system  ID.   Changing  a VG to not clustered will set the system ID to
       the host running the vgchange command.

   creation_host
       In vgcreate, the VG metadata field creation_host is set by  default  to
       the host's uname.  The creation_host cannot be changed, and is not used
       to control access.  When system_id_source is "uname", the system_id and
       creation_host fields will be the same.

   orphans
       Orphan  PVs  are unused devices; they are not currently used in any VG.
       Because of this, they are not protected by a system ID,  and  any  host
       can  use  them.   Coordination  of  changes to orphan PVs is beyond the
       scope of system ID.  The same is true of any block device that is not a
       PV.

SEE ALSO
       vgcreate(8),   vgchange(8),   vgimport(8),  vgexport(8),  vgs(8),  lvm-
       lockd(8), lvm.conf(5), machine-id(5), uname(2)

Red Hat, Inc           LVM TOOLS 2.03.07(2) (2019-11-30)        LVMSYSTEMID(7)

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