source: gpfs_3.1_ker2.6.20/share/man/man8/mmcrsnapshot.8 @ 47

.TH mmcrsnapshot 02/16/06

mmcrsnapshot Command

.SH "Name"

.PP

\fBmmcrsnapshot\fR - Creates a snapshot of an entire GPFS file system

at a single point in time.

.SH "Synopsis"

.PP

\fBmmcrsnapshot\fR \fIDevice\fR \fIDirectory\fR

.SH "Description"

.PP

Use the \fBmmcrsnapshot\fR command to create a snapshot of an entire

GPFS file system at a single point in time.

.PP

A snapshot is a copy of the changed user data in the file system.

System data and existing snapshots are not copied. The snapshot

function allows a backup or mirror program to run concurrently with user

updates and still obtain a consistent copy of the file system as of the time

the copy was created. Snapshots are exact copies of changed data in the

active files and directories of a file system. Snapshots of a file

system are read-only and are stored in a \fB.snapshots\fR

directory. The files and attributes of the file system may be changed

only in the active copy.

.PP

There is a maximum limit of 31 snapshots per file system. Snapshots may

be deleted only by issuing the

\fBmmdelsnapshot\fR

command. The \fB.snapshots\fR directory cannot be

deleted.

.PP

If the \fBmmcrsnapshot\fR command is issued while a conflicting command

is running, the \fBmmcrsnapshot\fR command waits for that command to

complete. If the \fBmmcrsnapshot\fR command is running while a

conflicting command is issued, the conflicting command waits for the

\fBmmcrsnapshot\fR command to complete. Conflicting operations

include: 

.RS +3

.HP 3

1. Other snapshot commands

.HP 3

2. Adding, deleting, replacing disks in the file system

.HP 3

3. Rebalancing, repairing, reducing disk fragmentation in a file system

.RE

.PP

If quorum is lost before the \fBmmcrsnapshot\fR command completes, the

snapshot is considered partial and will be deleted when quorum is achieved

again.

.PP

Because snapshots are not copies of the entire file system, they should not

be used as protection against media failures. For protection against

media failures, see

\fIGeneral Parallel File

System: Concepts, Planning, and Installation Guide\fR and search

on \fIrecoverability considerations\fR.

.SH "Parameters"

.PP

.RS +3

\fB\fIDevice\fR

\fR

.RE

.RS +9

The device name of the file system for which the snapshot is to be

created. File system names need not be fully-qualified.

\fBfs0\fR is just as acceptable as \fB/dev/fs0\fR.

.PP

This must be the first parameter.

.RE

.PP

.RS +3

\fB\fIDirectory\fR

\fR

.RE

.RS +9

The subdirectory name where the snapshots are stored.

.PP

This is a subdirectory of the root directory and must be a unique name

within the root directory. If you do not want to traverse the root to

access the snapshot you can create a symbolic link to the snapshot by issuing

the

\fBmmsnapdir\fR command.

.RE

.SH "Options"

.PP

NONE

.SH "Exit status"

.PP

.PP

.RS +3

\fB0

\fR

.RE

.RS +9

Successful completion.

.RE

.PP

.RS +3

\fBnonzero

\fR

.RE

.RS +9

A failure has occurred.

.RE

.SH "Security"

.PP

You must have root authority to run the \fBmmcrsnapshot\fR

command.

.PP

You may issue the \fBmmcrsnapshot\fR command from any node in the GPFS

cluster.

.PP

When using the \fBrcp\fR and \fBrsh\fR commands for remote

communication, a properly configured \fB.rhosts\fR file must exist

in the root user's home directory on each node in the GPFS

cluster. If you have designated the use of a different remote

communication program on either the

\fBmmcrcluster\fR

or the

\fBmmchcluster\fR command, you must

ensure:

.RS +3

.HP 3

1. Proper authorization is granted to all nodes in the GPFS cluster.

.HP 3

2. The nodes in the GPFS cluster can communicate without the use of a

password, and without any extraneous messages.

.RE

.SH "Examples"

.PP

To create a snapshot \fBsnap1\fR, for the file system \fBfs1\fR,

issue this command:

.sp

.nf

mmcrsnapshot fs1 snap1

.fi

.sp

.PP

The output is similar to this:

.sp

.nf

Writing dirty data to disk

Quiescing all file system operations

Writing dirty data to disk again

Creating snapshot.

Resuming operations.

.fi

.sp

.PP

Before issuing the command, the directory structure would appear similar

to:

.sp

.nf

/fs1/file1

/fs1/userA/file2

/fs1/userA/file3

.fi

.sp

.PP

After the command has been issued, the directory structure would appear

similar to:

.sp

.nf

/fs1/file1

/fs1/userA/file2

/fs1/userA/file3

/fs1/.snapshots/snap1/file1

/fs1/.snapshots/snap1/userA/file2

/fs1/.snapshots/snap1/userA/file3

.fi

.sp

.PP

If a second snapshot were to be created at a later time, the first snapshot

would remain as is. Snapshots are made only of active file systems, not

existing snapshots. For example:

.sp

.nf

mmcrsnapshot fs1 snap2

.fi

.sp

.PP

The output is similar to this:

.sp

.nf

Writing dirty data to disk

Quiescing all file system operations

Writing dirty data to disk again

Creating snapshot.

Resuming operations.

.fi

.sp

.PP

After the command has been issued, the directory structure would appear

similar to:

.sp

.nf

/fs1/file1

/fs1/userA/file2

/fs1/userA/file3

/fs1/.snapshots/snap1/file1

/fs1/.snapshots/snap1/userA/file2

/fs1/.snapshots/snap1/userA/file3

/fs1/.snapshots/snap2/file1

/fs1/.snapshots/snap2/userA/file2

/fs1/.snapshots/snap2/userA/file3

.fi

.sp

.SH "See also"

.PP

mmdelsnapshot Command

.PP

mmlssnapshot Command

.PP

mmrestorefs Command

.PP

mmsnapdir Command

.SH "Location"

.PP

\fB/usr/lpp/mmfs/bin\fR

.PP