1LVMSYSTEMID(7) LVMSYSTEMID(7)
2
6 lvmsystemid — LVM system ID
7
10 The lvm(8) system ID restricts Volume Group (VG) access to one host.
11 This is useful when a VG is placed on shared storage devices, or when
12 local devices are visible to both host and guest operating systems. In
13 cases like these, a VG can be visible to multiple hosts at once, and
14 some mechanism is needed to protect it from being used by more than one
15 host at a time.
16 A VG's system ID identifies one host as the VG owner. The host with a
18 matching system ID can use the VG and its LVs, while LVM on other hosts
19 will ignore it. This protects the VG from being accidentally used from
20 other hosts.
21 The system ID is a string that uniquely identifies a host. It can be
23 configured as a custom value, or it can be assigned automatically by
24 LVM using some unique identifier already available on the host, e.g.
25 machine-id or uname.
26 When a new VG is created, the system ID of the local host is recorded
28 in the VG metadata. The creating host then owns the new VG, and LVM on
29 other hosts will ignore it. When an existing, exported VG is imported
30 (vgimport), the system ID of the local host is saved in the VG meta‐
31 data, and the importing host owns the VG.
32 A VG without a system ID can be used by LVM on any host where the VG's
34 devices are visible. When system IDs are not used, device filters
35 should be configured on all hosts to exclude the VG's devices from all
36 but one host.
37 A foreign VG is a VG seen by a host with an unmatching system ID, i.e.
39 the system ID in the VG metadata does not match the system ID config‐
40 ured on the host. If the host has no system ID, and the VG does, the
41 VG is foreign and LVM will ignore it. If the VG has no system ID, ac‐
42 cess is unrestricted, and LVM can access it from any host, whether the
43 host has a system ID or not.
44 Changes to a host's system ID and a VG's system ID can be made in lim‐
46 ited circumstances (see vgexport and vgimport). Improper changes can
47 result in a host losing access to its VG, or a VG being accidentally
48 damaged by access from an unintended host. Even limited changes to the
49 VG system ID may not be perfectly reflected across hosts. A more co‐
50 herent view of shared storage requires an inter-host locking system to
51 coordinate access.
52 Valid system ID characters are the same as valid VG name characters.
54 If a system ID contains invalid characters, those characters are omit‐
55 ted and remaining characters are used. If a system ID is longer than
56 the maximum name length, the characters up to the maximum length are
57 used. The maximum length of a system ID is 128 characters.
58 Print the system ID of a VG to check if it is set:
60 vgs -o systemid VG
62 Print the system ID of the local host to check if it is configured:
64 lvm systemid
66 Limitations and warnings
69 To benefit fully from system ID, all hosts should have a system ID con‐
70 figured, and all VGs should have a system ID set. Without any method
71 to restrict access, e.g. system ID or device filters, a VG that is vis‐
72 ible to multiple hosts can be accidentally damaged or destroyed.
73 • A VG without a system ID can be used without restriction from any
76 host where it is visible, even from hosts that have a system ID.
77 • Many VGs will not have a system ID set because LVM has not enabled it
80 by default, and even when enabled, many VGs were created before the
81 feature was added to LVM or enabled. A system ID can be assigned to
82 these VGs by using vgchange --systemid (see below).
83 • Two hosts should not be assigned the same system ID. Doing so de‐
86 feats the purpose of distinguishing different hosts with this value.
87 • Orphan PVs (or unused devices) on shared storage are unprotected by
90 the system ID feature. Commands that use these PVs, such as vgcreate
91 or vgextend, are not prevented from performing conflicting operations
92 and corrupting the PVs. See the orphans section for more informa‐
93 tion.
94 • The system ID does not protect devices in a VG from programs other
97 than LVM.
98 • A host using an old LVM version (without the system ID feature) will
101 not recognize a system ID set in VGs. The old LVM can read a VG with
102 a system ID, but is prevented from writing to the VG (or its LVs).
103 The system ID feature changes the write mode of a VG, making it ap‐
104 pear read-only to previous versions of LVM.
105 This also means that if a host downgrades to the old LVM version, it
107 would lose access to any VGs it had created with a system ID. To
108 avoid this, the system ID should be removed from local VGs before
109 downgrading LVM to a version without the system ID feature.
110 Types of VG access
114 A local VG is meant to be used by a single host.
115 A shared or clustered VG is meant to be used by multiple hosts.
117 These can be further distinguished as:
119 Unrestricted: A local VG that has no system ID. This VG type is unpro‐
121 tected and accessible to any host.
122 Owned: A local VG that has a system ID set, as viewed from the host
124 with a matching system ID (the owner). This VG type is acessible to
125 the host.
126 Foreign: A local VG that has a system ID set, as viewed from any host
128 with an unmatching system ID (or no system ID). It is owned by another
129 host. This VG type is not accessible to the host.
130 Exported: A local VG that has been exported with vgexport and has no
132 system ID. This VG type can only be accessed by vgimport which will
133 change it to owned.
134 Shared: A shared or "lockd" VG has the lock_type set and has no system
136 ID. A shared VG is meant to be used on shared storage from multiple
137 hosts, and is only accessible to hosts using lvmlockd. Applicable only
138 if LVM is compiled with lvmlockd support.
139 Clustered: A clustered or "clvm" VG has the clustered flag set and has
141 no system ID. A clustered VG is meant to be used on shared storage
142 from multiple hosts, and is only accessible to hosts using clvmd. Ap‐
143 plicable only if LVM is compiled with clvm support.
144 Host system ID configuration
148 A host's own system ID can be defined in a number of ways. lvm.conf
149 global/system_id_source defines the method LVM will use to find the lo‐
150 cal system ID:
151 none
154 LVM will not use a system ID. LVM is allowed to access VGs
156 without a system ID, and will create new VGs without a system
157 ID. An undefined system_id_source is equivalent to none.
158 lvm.conf
160 global {
161 system_id_source = "none"
162 }
163 machineid
166 The content of /etc/machine-id is used as the system ID if
168 available. See machine-id(5) and systemd-machine-id-setup(1) to
169 check if machine-id is available on the host.
170 lvm.conf
172 global {
173 system_id_source = "machineid"
174 }
175 uname
178 The string utsname.nodename from uname(2) is used as the system
180 ID. A uname beginning with "localhost" is ignored and equiva‐
181 lent to none.
182 lvm.conf
184 global {
185 system_id_source = "uname"
186 }
187 lvmlocal
190 The system ID is defined in lvmlocal.conf local/system_id.
192 lvm.conf
194 global {
195 system_id_source = "lvmlocal"
196 }
197 lvmlocal.conf
199 local {
200 system_id = "example_name"
201 }
202 file
205 The system ID is defined in a file specified by lvm.conf
207 global/system_id_file.
208 lvm.conf
210 global {
211 system_id_source = "file"
212 system_id_file = "/path/to/file"
213 }
214 Changing system_id_source will likely cause the system ID of the host
217 to change, which will prevent the host from using VGs that it previ‐
218 ously used (see extra_system_ids below to handle this.)
219 If a system_id_source other than none fails to produce a system ID
221 value, it is the equivalent of having none. The host will be allowed
222 to access VGs with no system ID, but will not be allowed to access VGs
223 with a system ID set.
224 Overriding system ID
228 In some cases, it may be necessary for a host to access VGs with dif‐
229 ferent system IDs, e.g. if a host's system ID changes, and it wants to
230 use VGs that it created with its old system ID. To allow a host to ac‐
231 cess VGs with other system IDs, those other system IDs can be listed in
232 lvmlocal.conf local/extra_system_ids.
233 lvmlocal.conf
235 local {
236 extra_system_ids = [ "my_other_name" ]
237 }
238 A safer option may be configuring the extra values as needed on the
240 command line as:
241 --config 'local/extra_system_ids=["id"]'
242 vgcreate
246 In vgcreate, the host running the command assigns its own system ID to
247 the new VG. To override this and set another system ID:
248 vgcreate --systemid SystemID VG PVs
250 Overriding the host's system ID makes it possible for a host to create
252 a VG that it may not be able to use. Another host with a system ID
253 matching the one specified may not recognize the new VG without manu‐
254 ally rescanning devices.
255 If the --systemid argument is an empty string (""), the VG is created
257 with no system ID, making it accessible to other hosts (see warnings
258 above.)
259 report/display
263 The system ID of a VG is displayed with the "systemid" reporting op‐
264 tion.
265 Report/display commands ignore foreign VGs by default. To report for‐
267 eign VGs, the --foreign option can be used. This causes the VGs to be
268 read from disk.
269 vgs --foreign -o +systemid
271 When a host with no system ID sees foreign VGs, it warns about them as
273 they are skipped. The host should be assigned a system ID, after which
274 standard reporting commands will silently ignore foreign VGs.
275 vgexport/vgimport
279 vgexport clears the VG system ID when exporting the VG.
280 vgimport sets the VG system ID to the system ID of the host doing the
282 import.
283 vgchange
287 A host can change the system ID of its own VGs, but the command re‐
288 quires confirmation because the host may lose access to the VG being
289 changed:
290 vgchange --systemid SystemID VG
292 The system ID can be removed from a VG by specifying an empty string
294 ("") as the new system ID. This makes the VG accessible to other hosts
295 (see warnings above.)
296 A host cannot directly change the system ID of a foreign VG.
298 To move a VG from one host to another, vgexport and vgimport should be
300 used.
301 To forcibly gain ownership of a foreign VG, a host can temporarily add
303 the foreign system ID to its extra_system_ids list, and change the sys‐
304 tem ID of the foreign VG to its own. See Overriding system ID above.
305 shared VGs
309 A shared VG has no system ID set, allowing multiple hosts to use it via
310 lvmlockd. Changing a VG to shared will clear the existing system ID.
311 Applicable only if LVM is compiled with lvmlockd support.
312 clustered VGs
316 A clustered/clvm VG has no system ID set, allowing multiple hosts to
317 use it via clvmd. Changing a VG to clustered will clear the existing
318 system ID. Changing a VG to not clustered will set the system ID to
319 the host running the vgchange command.
320 creation_host
324 In vgcreate, the VG metadata field creation_host is set by default to
325 the host's uname. The creation_host cannot be changed, and is not used
326 to control access. When system_id_source is "uname", the system_id and
327 creation_host fields will be the same.
328 orphans
331 Orphan PVs are unused devices; they are not currently used in any VG.
332 Because of this, they are not protected by a system ID, and any host
333 can use them. Coordination of changes to orphan PVs is beyond the
334 scope of system ID. The same is true of any block device that is not a
335 PV.
336
339 vgcreate(8), vgchange(8), vgimport(8), vgexport(8), vgs(8), lvm‐
340 lockd(8), lvm.conf(5), machine-id(5), uname(2)
341Red Hat, Inc LVM TOOLS 2.03.11(2) (2021-01-08) LVMSYSTEMID(7)