source: gpfs_3.1_ker2.6.20/share/man/man8/mmcrsnapshot.8 @ 173

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1.TH mmcrsnapshot 02/16/06
2mmcrsnapshot Command
3.SH "Name"
4.PP
5\fBmmcrsnapshot\fR - Creates a snapshot of an entire GPFS file system
6at a single point in time.
7.SH "Synopsis"
8.PP
9\fBmmcrsnapshot\fR \fIDevice\fR \fIDirectory\fR
10.SH "Description"
11.PP
12Use the \fBmmcrsnapshot\fR command to create a snapshot of an entire
13GPFS file system at a single point in time.
14.PP
15A snapshot is a copy of the changed user data in the file system.
16System data and existing snapshots are not copied. The snapshot
17function allows a backup or mirror program to run concurrently with user
18updates and still obtain a consistent copy of the file system as of the time
19the copy was created. Snapshots are exact copies of changed data in the
20active files and directories of a file system. Snapshots of a file
21system are read-only and are stored in a \fB.snapshots\fR
22directory. The files and attributes of the file system may be changed
23only in the active copy.
24.PP
25There is a maximum limit of 31 snapshots per file system. Snapshots may
26be deleted only by issuing the
27\fBmmdelsnapshot\fR
28command. The \fB.snapshots\fR directory cannot be
29deleted.
30.PP
31If the \fBmmcrsnapshot\fR command is issued while a conflicting command
32is running, the \fBmmcrsnapshot\fR command waits for that command to
33complete. If the \fBmmcrsnapshot\fR command is running while a
34conflicting command is issued, the conflicting command waits for the
35\fBmmcrsnapshot\fR command to complete. Conflicting operations
36include:
37.RS +3
38.HP 3
391. Other snapshot commands
40.HP 3
412. Adding, deleting, replacing disks in the file system
42.HP 3
433. Rebalancing, repairing, reducing disk fragmentation in a file system
44.RE
45.PP
46If quorum is lost before the \fBmmcrsnapshot\fR command completes, the
47snapshot is considered partial and will be deleted when quorum is achieved
48again.
49.PP
50Because snapshots are not copies of the entire file system, they should not
51be used as protection against media failures. For protection against
52media failures, see
53\fIGeneral Parallel File
54System: Concepts, Planning, and Installation Guide\fR and search
55on \fIrecoverability considerations\fR.
56.SH "Parameters"
57.PP
58.RS +3
59\fB\fIDevice\fR
60\fR
61.RE
62.RS +9
63The device name of the file system for which the snapshot is to be
64created. File system names need not be fully-qualified.
65\fBfs0\fR is just as acceptable as \fB/dev/fs0\fR.
66.PP
67This must be the first parameter.
68.RE
69.PP
70.RS +3
71\fB\fIDirectory\fR
72\fR
73.RE
74.RS +9
75The subdirectory name where the snapshots are stored.
76.PP
77This is a subdirectory of the root directory and must be a unique name
78within the root directory. If you do not want to traverse the root to
79access the snapshot you can create a symbolic link to the snapshot by issuing
80the
81\fBmmsnapdir\fR command.
82.RE
83.SH "Options"
84.PP
85NONE
86.SH "Exit status"
87.PP
88.PP
89.RS +3
90\fB0
91\fR
92.RE
93.RS +9
94Successful completion.
95.RE
96.PP
97.RS +3
98\fBnonzero
99\fR
100.RE
101.RS +9
102A failure has occurred.
103.RE
104.SH "Security"
105.PP
106You must have root authority to run the \fBmmcrsnapshot\fR
107command.
108.PP
109You may issue the \fBmmcrsnapshot\fR command from any node in the GPFS
110cluster.
111.PP
112When using the \fBrcp\fR and \fBrsh\fR commands for remote
113communication, a properly configured \fB.rhosts\fR file must exist
114in the root user's home directory on each node in the GPFS
115cluster. If you have designated the use of a different remote
116communication program on either the
117\fBmmcrcluster\fR
118or the
119\fBmmchcluster\fR command, you must
120ensure:
121.RS +3
122.HP 3
1231. Proper authorization is granted to all nodes in the GPFS cluster.
124.HP 3
1252. The nodes in the GPFS cluster can communicate without the use of a
126password, and without any extraneous messages.
127.RE
128.SH "Examples"
129.PP
130To create a snapshot \fBsnap1\fR, for the file system \fBfs1\fR,
131issue this command:
132.sp
133.nf
134mmcrsnapshot fs1 snap1
135.fi
136.sp
137.PP
138The output is similar to this:
139.sp
140.nf
141Writing dirty data to disk
142Quiescing all file system operations
143Writing dirty data to disk again
144Creating snapshot.
145Resuming operations.
146.fi
147.sp
148.PP
149Before issuing the command, the directory structure would appear similar
150to:
151.sp
152.nf
153/fs1/file1
154/fs1/userA/file2
155/fs1/userA/file3
156.fi
157.sp
158.PP
159After the command has been issued, the directory structure would appear
160similar to:
161.sp
162.nf
163/fs1/file1
164/fs1/userA/file2
165/fs1/userA/file3
166/fs1/.snapshots/snap1/file1
167/fs1/.snapshots/snap1/userA/file2
168/fs1/.snapshots/snap1/userA/file3
169.fi
170.sp
171.PP
172If a second snapshot were to be created at a later time, the first snapshot
173would remain as is. Snapshots are made only of active file systems, not
174existing snapshots. For example:
175.sp
176.nf
177mmcrsnapshot fs1 snap2
178.fi
179.sp
180.PP
181The output is similar to this:
182.sp
183.nf
184Writing dirty data to disk
185Quiescing all file system operations
186Writing dirty data to disk again
187Creating snapshot.
188Resuming operations.
189.fi
190.sp
191.PP
192After the command has been issued, the directory structure would appear
193similar to:
194.sp
195.nf
196/fs1/file1
197/fs1/userA/file2
198/fs1/userA/file3
199/fs1/.snapshots/snap1/file1
200/fs1/.snapshots/snap1/userA/file2
201/fs1/.snapshots/snap1/userA/file3
202/fs1/.snapshots/snap2/file1
203/fs1/.snapshots/snap2/userA/file2
204/fs1/.snapshots/snap2/userA/file3
205.fi
206.sp
207.SH "See also"
208.PP
209mmdelsnapshot Command
210.PP
211mmlssnapshot Command
212.PP
213mmrestorefs Command
214.PP
215mmsnapdir Command
216.SH "Location"
217.PP
218\fB/usr/lpp/mmfs/bin\fR
219.PP
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