1fence_scsi(8) System Manager's Manual fence_scsi(8)
3
7 fence_scsi - I/O fencing agent for SCSI persistent reservations
8
11 fence_scsi [OPTION]...
12
15 fence_scsi is an I/O fencing agent which can be used with the SCSI
16 devices that support persistent reservations (SPC-2 or greater).
17 SCSI persistent reservations work by having each node in the cluster
19 register with the SCSI device. Registration is done using a unique key
20 (based on the node's IP address). Each node that will perform I/O oper‐
21 ations to the shared storage must register with the device. This is
22 done at system startup with the scsi_reserve init script. This script
23 will discover all clustered volumes as well as the underlying SCSI
24 device(s). Device discovery is done via the lvs command (see lvs(8))
25 and is subject to any filtering rules defined in the lvm.conf file.
26 After generating the node's unique key, the script will register the
28 node with the SCSI device(s) that were discovered. Once the node is
29 registered, the script will attempt to create a reservation. Unlike
30 registrations, of which there are multiple registrants (one for each
31 node in the cluster), there is only one reservation holder. If a reser‐
32 vation does not already exist for a device, the script will create a
33 reservation using the node's unique key.
34 It is important to distinguish between registrations and reservations.
36 As mentioned above, each node that will perform I/O operations to the
37 SCSI device must register. As a result, there will be multiple regis‐
38 trations for a given SCSI device. In contrast, there can only be one
39 reservation per SCSI device. It is not important which node holds the
40 reservation. The reservation simply tells the device how the regis‐
41 trants are allowed to access the device. For our purposes, the reserva‐
42 tion type is "write exclusive, registrants only". With this reserva‐
43 tion type, only registered nodes will be able to write to the device.
44 When the cluster must fence a node, it simply revokes a node's regis‐
46 tration, or "unregisters" the node. This operation also uses the node's
47 unique key. By deriving the unique key based on the errant node's IP
48 address, the cluster can "unregister" the key. As a result, the errant
49 node will no longer be able to write to the SCSI device.
50 Note that the node that holds the reservation for a device must also be
52 registered with that device. When the situation arises where the node
53 that is being fenced is also the reservation holder, the reservation
54 must be moved. This is handled by using the "preempt-and-abort command"
55 which will transfer the reservation from the node that is being fenced
56 to the node that is performing the fencing. This operation will main‐
57 tain the reservation while "unregistering" the node being fenced.
58 At system shutdown, the scsi_reserve script will attempt to "unregis‐
60 ter" the node from all devices. The exception is when the node happens
61 to be the reservation holder. In this case, the script does nothing,
62 due to the fact that there may be other nodes using the device and the
63 reservation must remain intact.
64 fence_scsi accepts options on the command line as well as from stdin.
66 fenced sends parameters through stdin when it execs the agent.
67 fence_scsi can be run by itself with command line options. This is
68 useful for testing and for turning outlets on or off from scripts.
69
72 -n node
73 Name of the node to be fenced.
74 -h Print out a help message describing available options, then
76 exit.
77 -s self
79 Name of the node that will perform the fencing operation.
80 -v Verbose output.
82 -V Print out a version message, then exit.
84
87 agent = < param >
88 This option is used by fence_node(8) and is ignored by
89 fence_scsi.
90 nodename = < hostname | ip >
92 Name of the node to be fenced.
93 self = < nodename >
95 Name of the node that will perform the fencing operation.
96 verbose = < param >
98 Verbose output.
99
102 fence(8), fence_node(8), sg_persist(8), lvs(8), lvm.conf(5)
103 fence_scsi(8)