AIX JFS2 snapshots

There are two types of snapshots available in AIX:

• External snapshots (starting from AIX 5.2 with patch 5200-01  or later)
• Internal snapshots (AIX 6.1)

Both are documented extremely poorly. I hope that this page and a companion page about chfs command will help to use this feature more widely.

External snapshots

File system snapshots are available from AIX 5L v5.2 in JFS2 file systems. Snapshots had to be created in a separate logical volume (in mirrored drive pair). This is called “JFS2 External Snapshot”. External snapshots are created with chfs command

After creation the  snapshot remains static and it retains all the information form the  original file system (called the snappedFS) including security permissions. You can create a JFS2 snapshot without unmounting or quiescing the file system. You can use a JFS2 snapshot to use as an online backup of the file system, to access the files or directories as they existed when the snapshot was taken, or to back up to removable media.

Note the following about JFS2 snapshots:

• A snapshot image of the root (/) or /usr file system is overwritten when the system is rebooted. Snapshots of other file systems can be preserved by unmounting the file system before rebooting. Snapshots created in AIX 5.2 with 5200-01 are recoverable: you can run fsck on them. When fsck or logredo runs on a JFS2 filesystem with a snapshot created, the snapshot will be preserved.
• Running the defragfs command against a file system with snapshots is not recommended. Every block that is moved during defragmentation must also be copied to the snapshot, which is both time consuming and a waste of space in the snapshot logical volume.
• If a snapshot runs out of space, all snapshots for that snappedFS are deleted. This failure writes an entry to the error log.
• If a write to a snapshot fails, all snapshots for that snappedFS are deleted. This failure writes an entry to the error log.

Internal snapshots

Starting from AIX V6.1 IBM offers the ability to create snapshots with the file system (internal snapshots). These internal snapshots are stored under /fsmountpoint/.snapshot/snapshotname.

Both the internal and the external snapshots keep track of the changes to the snapped file system by saving the modified or deleted file blocks. Snapshots provide point-in-time (PIT) images of the source file system. Basically snapshots are used for taking PIT images (backup) of a file system during production runtime.

Advantages of Internal Snapshot:

a) No super user permissions are necessary to access data from a snapshot, since no initial mount operation is required.
b) No additional file system or logical volume needs to be maintained and monitored.
c) Snapshots are easily NFS exported, since they are in held in the same filesystem.

Management of Internal snapshots:

A JFS2 file system must be created with the new -a isnapshot=yes option. Existing file systems created without the isnapshot option cannot be used for internal snapshots. They have to be recreated or have to use external snapshots.

To create an internal snapshot:

# snapshot -o snapfrom=/oracle -n snap10
Snapshot "snap10" for file system /oracle created.

To create an external snapshot:
# snapshot -o snapfrom=/oralce /dev/snaporacle
This command creates a snapshot for the /oracle file system on the /dev/snaporacle logical volume, which already exists.

To list all snapshots for a file system:

# snapshot –q /oracle
Snapshots for /oracle
Current Name Time
* snap10 Mon Dec 15 09:17:51 CDT 2008

Files under this snapshot “snap10” are available under /oracle/.snapshot/snap10 directory. These files are read only; no modifications are allowed.

To delete an internal snapshot:

# snapshot –d –n snap10 /oracle


SMIT Screens:

To access smitty menu items, following the below steps

smitty> system storage management> file systems> add change show delete filesystems> enhanced journaled filesystems

shows the below options

List Snapshots for an Enhanced Journaled File System
Create Snapshot for an Enhanced Journaled File System
Mount Snapshot for an Enhanced Journaled File System
Remove Snapshot for an Enhanced Journaled File System
Unmount Snapshot for an Enhanced Journaled File System
Change Snapshot for an Enhanced Journaled File System
Rollback an Enhanced Journaled File System to a Snapshot

Some points on Internal snapshots:

1. A snapped file system can be mounted read only on previous AIX 5L versions. The snapshot itself cannot be accessed. The file system must be in a clean state; run the fsck command to ensure that this is true.

2. A file system created with the ability for internal snapshots can still have external snapshots.

3. Once a file system has been enabled to use internal snapshots, this cannot be undone.

4. If the fsck command has to modify the file system, any internal snapshots for the file system will be deleted by fsck.

5. Snapped file systems cannot be shrunk.

6. The defragfs command cannot be run on a file system with internal snapshots.


Some points on Internal and External snapshots:

1. A file system can use exclusively one type of snapshot at the same time.

2. External snapshots are persistent across a system reboot.

3. Typically, a snapshot will need two to six percent of the space needed for the snapped file system. For a highly active file system, 15 percent is estimated.

4. During the creation of a snapshots, only read access to the snapped file system is allowed.

5. There is reduced performance for write operations to a snapped file system. Read operations are not affected.

6. Snapshots are not replacement for backups. A snapshot depends always on the snapped file system, while backups have no dependencies on the source.

7. Neither the mksysb nor alt_disk_install commands will preserve snapshots.

8. A file system with snapshots cannot be managed by DMAPI. A file system being managed by DMAPI cannot create a snapshot

NEWS CONTENTS

• 200102 : IBM - JFS2 Snapshot Quick Reference ( IBM - JFS2 Snapshot Quick Reference, )
• 200102 : Help - ( Help -, )
• 200102 : Help - ( Help -, )
• 200102 : How to use snapshot - Toolbox for IT Groups ( How to use snapshot - Toolbox for IT Groups, )
• 200102 : Maintaining File Systems Tasks ( )
• 200102 : Re: problem splitting off a copy of a JFS2 filesystem ... ( )
• 200102 : Help - Making an online backup of a JFS ( Help - Making an online backup of a JFS, )
• 200102 : AIXchange Snapshots Make File Recovery a Snap ( AIXchange Snapshots Make File Recovery a Snap, )
• 200102 : How to use snapshot - Toolbox for IT Groups ( How to use snapshot - Toolbox for IT Groups, )
• 200102 : Snapshot in AIX 5.2 - Dev Archives ( Snapshot in AIX 5.2 - Dev Archives, )
• 200102 : how to use jfs2 snapshots- - Toolbox for IT Groups ( how to use jfs2 snapshots- - Toolbox for IT Groups, )

Old News ;-)

IBM - JFS2 Snapshot Quick Reference

Technote (FAQ)

Question

This document is a quick guide to using snapshots of JFS2 filesystems

Answer

The JFS2 snapshot command will create an image of a filesystem at a point in time, allowing the user to back up data from the snapshot rather than from the original filesystem. This allows backing up data without having to stop using it first.
The concept used in the snapped filesystem is "copy on write". During creation of the snapshot filesystem the source filesystem is quiesced while the copy is made, to insure a proper copy. Then only the filesystem structure is created. When any modification is done to the source system, such as a write of data or delete, the original data is copied into the snapped filesystem.

Usually a snapshot filesystem will only need to be 2-6% of the size of the original filesystem, due to this copy-on-write feature.

* Creating a snapshot:
Find out the size of the filesystem:

# lsfs -q /origfs
Name Nodename Mount Pt VFS Size Options Auto
Accounting
/dev/fslv02 -- /origfs jfs2 4194304 rw,cio no
no
(lv size: 4194304, fs size: 4194304, block size: 4096, sparse files: yes, inline log: no, inline log size: 0, reserved: 0, reserved: 0, DMAPI: no, VIX: yes)

In the lsfs -q output the size is reported in 512-byte blocks. So in the above example the filesystem and logical volume are 2Gb in size. We'll make the snapshot filesystem 204Mb (10% of the original).

# snapshot -o snapfrom=/origfs -o size=419430
Snapshot for file system /origfs created on /dev/fslv05

* Mounting a snapshot:
# mount -v jfs2 -o snapshot /dev/fslv05 /mysnap

* Finding out if a fs has a snapshot already:
# snapshot -q /origfs

Snapshots for /origfs
Current Location 512-blocks Free Time
* /dev/fslv05 419430 418662 Fri Apr 21 08:30:36 PDT 2006

* Deleting a snapshot:

# snapshot -d /dev/fslv05
rmlv: Logical volume fslv05 is removed

For further information see the man page for the snapshot command.

Help -JFS online backups and JFS2 snapshots

You can make an point-in-time image of a JFS file system or of a JFS2 file system (AIX® 5.2 and later), which you can then use for backup purposes. There are differences, however, in the requirements and behavior of this image for each file system type.

For a JFS file system, you can split off a read-only static copy of a mirrored copy of the file system. Typically, a mirrored copy is updated whenever the original file system is updated, but this point-in-time copy does not change. It remains a stable image of the point in time at which the copy was made. When this image is used for backing up, any modifications that begin after you begin the procedure to create the image might not be present in the backup copy. Therefore, it is recommended that file system activity be minimal while the split is taking place. Any changes that occur after the split is made will not be present in the backup copy.

For a JFS2 file system, the point-in-time image is called a snapshot. The snapshot remains static and it retains the same security permissions as the original file system (called the snappedFS) had when the snapshot was made. Also, you can create a JFS2 snapshot without unmounting or quiescing the file system. You can use a JFS2 snapshot to use as an online backup of the file system, to access the files or directories as they existed when the snapshot was taken, or to back up to removable media. Note the following about JFS2 snapshots:

• A snapshot image of the root (/) or /usr file system is overwritten when the system is rebooted. Snapshots of other file systems can be preserved by unmounting the file system before rebooting. Snapshots created in AIX 5.2 with 5200-01 are recoverable. When fsck or logredo runs on a JFS2 filesystem with a snapshot created on AIX 5.2 with 5200-01, the snapshot will be preserved. A cleanly unmounted filesystem with an AIX 5.2-created snapshot will also be recoverable once it is mounted on an AIX 5.2 with 5200-01 system.
• Running the defragfs command against a file system with snapshots is not recommended. Every block that is moved during defragmentation must also be copied to the snapshot, which is both time consuming and a waste of space in the snapshot logical volume.
• If a snapshot runs out of space, all snapshots for that snappedFS are deleted. This failure writes an entry to the error log.
• If a write to a snapshot fails, all snapshots for that snappedFS are deleted. This failure writes an entry to the error log.
• A snapshot that is created or accessed on a AIX 5.2 with 5200-01 system cannot be accessed on an AIX 5.2 system. These snapshots must be deleted before the filesystem can be mounted.
• A JFS2 file system that has a snapshot on AIX 5.3 cannot be accessed on any releases prior to AIX 5.2 with 5200-01. If the system is to be moved back, the snapshots must be deleted first to allow file system access.

Help -JFS2 snapshots

You can make a point-in-time image of a JFS2 file system that you can then use for backup purposes.

The point-in-time image for a JFS2 file system is called a snapshot. The snapshot remains static and retains the same security permissions that the original file system (called the snappedFS) had when the snapshot was made. Also, you can create a JFS2 snapshot without unmounting the file system, or quiescing the file system. You can use a JFS2 snapshot to:

• Access the files or directories as they existed when the snapshot was taken.
• Backup to removable media.

There are two types of JFS2 snapshots: internal and external. A JFS2 external snapshot is created in a separate logical volume from the file system. The external snapshot can be mounted separately from the file system at its own unique mount point.

A JFS2 internal snapshot is created in the same logical volume as the file system and allocates blocks from the file system. An internal snapshot is accessible from the invisible .snapshot directory in the root of the JFS2 file system with the snapshot. A JFS2 file system must be enabled to support internal snapshots at the time the file system is created.

JFS2 snapshots do not support checking of file system quotas. You cannot use the repquota command on the snapshot to determine the state of the quota. The point-in-time quota information is preserved if you roll back the file system image to the snapshot image. Note the following considerations specific to JFS2 external snapshots and JFS2 internal snapshots:

• An external snapshot that is created or accessed on an AIX® 5.2 with 5200-01 system cannot be accessed on an AIX 5.2 system. These snapshots must be deleted before the file system can be mounted.
• A JFS2 file system that has a snapshot on AIX 5.3 cannot be accessed on any releases prior to AIX 5.2 with 5200-01. If the system is to be moved back, the snapshots must be deleted first to allow file system access.
• Running the defragfs command against a JFS2 file system with external snapshots is not recommended because every block that is moved during defragmentation must also be copied to the snapshot, which is both time consuming and a waste of space in the snapshot logical volume.
• If an external snapshot runs out of space, or if an external snapshot fails, all external snapshots for that snappedFS are marked invalid. Further access to the snapshot will fail. These failures write an entry to the error log.

Internal JFS2 snapshot considerations:

• Internal snapshots are preserved when the logredo command runs on a JFS2 file system with an internal snapshot.
• Internal snapshots are removed if the fsck command has to modify a JFS2 file system to repair it.
• If an internal snapshot runs out of space, or if a write to an internal snapshot fails, all internal snapshots for that snappedFS are marked invalid. Further access to the internal snapshots will fail. These failures write an entry to the error log.
• Internal snapshots are not separately mountable. You can access internal snapshots in the .snapshot directory of the root of the file system immediately after they are created. Consequently, you can access internal snapshots through an NFS server without having to export a separate mount point for the snapshot.
• Internal snapshots are not compatible with AIX releases prior to AIX 6.1. A JFS2 file system created to support internal snapshots cannot be modified on an earlier release of AIX.
• A JFS2 file system created to support internal snapshots is also enabled to support Extended Attributes Version 2.
• A JFS2 file system with internal snapshots cannot be used with a Data Management Application Programming Interface (DMAPI).
• You cannot use the defragfs command against a JFS2 file system with internal snapshots.
• The .snapshot directory is not returned from the readdir() system call. This prevents unintended visiting of the snapshots. Any system calls or commands that depend on the readdir() system call fail with the .snapshot directory (for example, the /bin/pwd command and the getcwd() system call of the .snapshot directory cannot find the parent directory).

How to use snapshot - Toolbox for IT Groups

"System Management Guide:
Operating System

and Devices
Make an Online Backup of a Mounted JFS or JFS2
Making an online backup of a mounted journaled file system (JFS or enhanced journaled file system (JFS2) creates a static image of the logical volume that contains the file system Th following procedures describe how to make an online backup=2 Which procedure you choose depends on whether the file system i a JFS or JFS2
Make an Online Backup of a JFS
To make an online backup of a mounted JFS, the logical volum that the file system resides on and the logical volume that it log resides on must be mirrored
Note:
Because the file writes are asynchronous, the split off cop might not contain all data that was written immediately befor the split Any modifications that begin after the split begin might not be present in the backup copy Therefore, it i recommended that file system activity be minimal while the spli is taking place
To split off a mirrored copy of the /home/xyz file system to new mount point named /jfsstaticcopy, type the following:
chfs -a splitcopy&H3D/jfsstaticcopy /home/xyz
You can control which mirrored copy is used as the backup b using the copy attribute The second mirrored copy is th default if a copy is not specified by the user For example:
chfs -a splitcopy&H3D/jfsstaticcopy -a copy&H3D1 /home/xyz
At this point, a read-only copy of the file system is availabl in /jfsstaticcopy Any changes made to the original file syste after the copy is split off are not reflected in the backu copy
To reintegrate the JFS split image as a mirrored copy at th /testcopy mount point, use the following command:
rmfs /testcopy
The rmfs command removes the file system copy from its split-of state and allows it to be reintegrated as a mirrored copy
Make and Back Up a Snapshot of a JFS2
Beginning with AIX 5 2, you can make a snapshot of a mounted JFS that establishes a consistent block-level image of the fil system at a point in time The snapshot image remains stabl even as the file system that was used to create the snapshot called the snappedFS, continues to change The snapshot retain the same security permissions as the snappedFS had when th snapshot was made
In the following scenario, you create a snapshot and back up th snapshot to removable media without unmounting or quiescing th file system, all with one command: backsnap You can also us the snapshot for other purposes, such as accessing the files o directories as they existed when the snapshot was taken You ca do the various snapshot procedures using Web-based Syste Manager, SMIT, or the backsnap and snapshot commands
To create a snapshot of the /home/abc/test file system and bac it up (by name) to the tape device /dev/rmt0, use the followin command:
backsnap -m /tmp/snapshot -s size&H3D16M -i f/dev/rmt /home/abc/test
This command creates a logical volume of 16 megabytes for th snapshot of the JFS2 file system (/home/abc/test) The snapsho is mounted on /tmp/snapshot and then a backup by name of th snapshot is made to the tape device After the backup completes the snapshot remains mounted Use the -R flag with the backsna command if you want the snapshot removed when the backu completes
"

Syntax of backnap command:

backsnap&H09Creates and backs up a JFS2 snapshot
backsnap -m /tmp/snapshot/data -s size&H3D16M -i -f /dev/rmt0 /dat : creates a 16 MB LV, creates a snapshot for the /data fil system on the created LV, mounts the snapshot o /tmp/snapshot/data and backups the files and directories in tha file system by name to /dev/rmt0

So, you can create a point in time copy of any given open Fil System of JFS2 type and move to a tape device You can als leave the copy in the snapshot file and the using a script wit cdcreate you can move the contens to a CD or DVD

Do you want to copy RDBMS files ??

Related White Papers and Webcasts

• Taking Role-Based Access Control to the Next Level

Maintaining File Systems Tasks

The simplest tasks you might need when maintaining file systems are grouped within this table.

1. For options, refer to the individual commands.
2. Do not change the names of system-critical file systems, which are / (root) on logical volume 4 (hd4), /usr on hd2, /var on hd9var, /tmp on hd3, and /blv on hd5. If you use the hdn convention, start at hd10.
3. Check the file systems before mounting by using the procedure File system verification or running the fsck command.
4. If an unmount fails, it might be because a user or process has an opened file in the file system being unmounted. The fuser command lets you find out which user or process might be causing the failure.
5. A file system group is a collection of file systems which have the same value for the type= identifier in the /etc/filesystems file.

• Recovering one or more files from an online external JFS2 snapshot
  You can replace a corrupted file if you have an accurate copy in an online external JFS2 snapshot.
• Recovering one or more files from an online internal JFS2 snapshot
  You can replace a corrupted file if you have an accurate copy in an online internal JFS2 snapshot.
• File systems on CD-ROM and DVD disks
  CDs and DVDs are not automatically mounted, but this feature can be enabled.
• Using file systems on read/write optical media
  CDRFS and JFS file systems can be used on read/write optical media.
• File system verification
  Inconsistencies can occur in file systems when the system is stopped while file systems remained mounted or when a disk is damaged. In such circumstances, it is important to verify file systems before mounting them.
• Reducing the size of a file system in your root volume group
  The simplest way to reduce all file systems to their minimum size is to set the SHRINK option to yes when restoring the base operating system from backup.

Re: problem splitting off a copy of a JFS2 filesystem ...

• From: "Sandor W. Sklar" <ssklar@xxxxxxxxxxxx>
• Date: Wed, 18 Apr 2007 09:42:10 -0700

Still not clear on why the instructions from the IBM documentation listed below don't work. I know that particular document is from the "AIX 5.3" manual section, but it also states specifically in there that it is valid for AIX 5.2. Maybe that's just an error in that document.

Thanks,
-s-

On Apr 18, 2007, at 6:52 AM, Rick Saylor wrote:

I ran into the same situation a couple of years ago. I worked with IBM support and they determined that with JFS2 file systems you have to the snapshot command, at least on AIX 5.2. I used the filesystem and volume group names from your email and incorporated them into the example below. It should work but I haven't tested it. You may have to change the number of logical partitions on the mklv command. I used 256 but you might have different needs.

To create your snapshot try:
1. mklv -y snaplv -t jfs2 emcvg 256
2. snapshot -o snapfrom=/s /dev/snaplv
3. mkdir /s_copy
4. mount -o snapshot /dev/snaplv /s_copy

To remove the snapshot:
1. umount /s_copy
2. snapshot -d /dev/snaplv
3. rmdir /s_copy

Again, please try this on a test system first.

I hope this helps,
Rick

At 04:55 PM 4/17/2007, you wrote:

I'm trying to split off a mirrored copy of a logical volume and mount
it as a separate (read-only ) filesystem, as described on the page:

<http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp? topic=/com.ibm.aix.baseadmn/doc/baseadmndita/ HT_baseadmn_snapshotjfs.htm>

... but it isn't working. That page says it should work on AIX 5.2,
but here's what I've got:

#> df /s
Filesystem 512-blocks Free %Used Iused %Iused Mounted on
/dev/lv21 209715200 65659248 69% 343096 5% /s

#> lsfs -q /s
Name Nodename Mount Pt VFS Size
Options Auto Accounting
/dev/lv21 -- /s jfs2 209715200
rw yes no
(lv size: 209715200, fs size: 209715200, block size: 4096, sparse
files: yes, inline log: yes, inline log size: 400, reserved: 0,
reserved: 0, DMAPI: no, VIX: no)

#> lslv lv21
LOGICAL VOLUME: lv21 VOLUME GROUP: emcvg
LV IDENTIFIER: 0001dcba00004c00000001047c9fe1c4.5
PERMISSION: read/write
VG STATE: active/complete LV STATE: opened/ syncd
TYPE: jfs2 WRITE VERIFY: off
MAX LPs: 512 PP SIZE: 512
megabyte(s)
COPIES: 2 SCHED POLICY: parallel
LPs: 200 PPs: 400
STALE PPs: 0 BB POLICY: relocatable
INTER-POLICY: minimum RELOCATABLE: yes
INTRA-POLICY: middle UPPER BOUND: 128
MOUNT POINT: /s LABEL: /s
MIRROR WRITE CONSISTENCY: on/ACTIVE
EACH LP COPY ON A SEPARATE PV ?: no
Serialize IO ?: NO

#> lsvg -l emcvg | grep lv21
lv21 jfs2 200 400 2 open/syncd /s
#> mkdir /s_copy

#> df /s_copy
Filesystem 512-blocks Free %Used Iused %Iused Mounted on
/dev/hd4 2621440 1475112 44% 3852 1% /
#> chfs -a splitcopy=/s_copy /s

#> echo $?
0

#> df /s_copy
Filesystem 512-blocks Free %Used Iused %Iused Mounted on
/dev/hd4 2621440 1475112 44% 3852 1% /

Note that the "chfs" command returns no error, and exits "0". The
split never happens though. Am I missing some crucial but non- obvious step here? This system is at:

#> oslevel -s
5200-09-04

... so I'm fairly up to date. Thanks in advance for the help ...
I've never done this before!

-s-

---------------------------------------------------------------------- ------
Rick Saylor Austin Community College Voice: (512) 223-1182
Director of System Services 9101 Tuscany Way Fax: (512) 223-1211
Information Technology Austin, Texas 78754

Help - Making an online backup of a JFS

Making an online backup of a mounted journaled file system (JFS) or enhanced journaled file system (JFS2) creates a static image of the logical volume that contains the file system.

To make an online backup of a mounted JFS, the logical volume that the file system resides on and the logical volume that its log resides on must be mirrored.

Note: Because the file writes are asynchronous, the split-off copy might not contain all data that was written immediately before the split. Any modifications that begin after the split begins might not be present in the backup copy. Therefore, it is recommended that file system activity be minimal while the split is taking place.

The information in this how-to scenario was tested using specific versions of AIX®. The results you obtain might vary significantly depending on your version and level of AIX.

To split off a mirrored copy of the /home/xyz file system to a new mount point named /jfsstaticcopy, type the following:

chfs -a splitcopy=/jfsstaticcopy /home/xyz

You can control which mirrored copy is used as the backup by using the copy attribute. The second mirrored copy is the default if a copy is not specified by the user. For example:

 chfs -a splitcopy=/jfsstaticcopy -a copy=1 /home/xyz

At this point, a read-only copy of the file system is available in /jfsstaticcopy. Any changes made to the original file system after the copy is split off are not reflected in the backup copy.

To reintegrate the JFS split image as a mirrored copy at the /testcopy mount point, use the following command:

 rmfs /testcopy

The rmfs command removes the file system copy from its split-off state and allows it to be reintegrated as a mirrored copy.

Parent topic: Storage management (Logical Volume Manager)

AIXchange Snapshots Make File Recovery a Snap

Watching this technical demo by Nigel Griffiths got me thinking. I like taking snapshots and flash copies on my external SAN devices. What if I want to take a snapshot of a file system on my AIX machine that isn't connected to a SAN?

Read more about these capabilities here.

http://publib.boulder.ibm.com/infocenter/systems/index.jsp?topic=/com.ibm.aix.baseadmn/doc/baseadmndita/jfs2_snapshots.htm

From the document:

"You can make a point-in-time image of a JFS2 file system that you can then use for backup purposes. The point-in-time image for a JFS2 file system is called a snapshot. The snapshot remains static and retains the same security permissions that the original file system (called the snappedFS) had when the snapshot was made. Also, you can create a JFS2 snapshot without unmounting the file system, or quiescing the file system. You can use a JFS2 snapshot to:

* Access the files or directories as they existed when the snapshot was taken.
* Backup to removable media.

"There are two types of JFS2 snapshots: internal and external. A JFS2 external snapshot is created in a separate logical volume from the file system. The external snapshot can be mounted separately from the file system at its own unique mount point."

So how do I do it? I'll duplicate what Nigel did in his video demo using my test machine that runs AIX 6.1.

First, I use the following command to create a file system in rootvg that's 500MB in size:

crfs -v jfs2 –g rootvg -a size=500M –m /snaptest -a isnapshot=yes

Then I mount the file system:

mount /snaptest

Then run two commands:

touch hello this is a test

echo "this is a test" > test.out

Finally, I run:

ls -la
drwxr-xr-x 3 root system 256 Oct 23 14:42 .
drwxr-xr-x 22 root system 4096 Oct 23 14:37 ..
-rw-r--r-- 1 root system 0 Oct 23 14:38 a
-rw-r--r-- 1 root system 0 Oct 23 14:38 hello
-rw-r--r-- 1 root system 0 Oct 23 14:38 is
drwxr-xr-x 2 root system 256 Oct 23 14:37 lost+found
-rw-r--r-- 1 root system 0 Oct 23 14:38 test
-rw-r--r-- 1 root system 15 Oct 23 14:42 test.out
-rw-r--r-- 1 root system 0 Oct 23 14:38 this

To see the available menu options, go here:

smitty > system storage management > file systems > add change show delete filesystems > enhanced journaled filesystems

The menu options are:

List Snapshots for an Enhanced Journaled File System
Create Snapshot for an Enhanced Journaled File System
Mount Snapshot for an Enhanced Journaled File System
Remove Snapshot for an Enhanced Journaled File System
Unmount Snapshot for an Enhanced Journaled File System
Change Snapshot for an Enhanced Journaled File System
Rollback an Enhanced Journaled File System to a Snapshot

In our case we want to create a snapshot. This can also be done from the command line:

snapshot -o snapfrom=/snaptest –n testsnap

Running ls –la reveals no additions in the file system, but if you cd to .snapshot, you'll find the files you just created.

I cd into /snaptest/.snapshot/testsnap and run ls to find all of the files that were in my file system when I took the snapshot.

Creating a snapshot allows you to easily recover files should someone delete them, without having to resort to restoring from a TSM machine or some other backup mechanism.

How to use snapshot - Toolbox for IT Groups

Reply from cdelgadop
on 4/15/2006 10:49 AM

Hi

You can use snapshots for many things including taking backups=2 From the IBM Documentation:

"System Management Guide:
Operating System and Devices

Make an Online Backup of a Mounted JFS or JFS2

Making an online backup of a mounted journaled file system (JFS or enhanced journaled file system (JFS2) creates a static image of the logical volume that contains the file system.

Th following procedures describe how to make an online backup=2 Which procedure you choose depends on whether the file system i a JFS or JFS2
Make an Online Backup of a JFS

To make an online backup of a mounted JFS, the logical volume that the file system resides on and the logical volume that it log resides on must be mirrored
Note:
Because the file writes are asynchronous, the split off cop might not contain all data that was written immediately befor the split Any modifications that begin after the split begin might not be present in the backup copy Therefore, it i recommended that file system activity be minimal while the spli is taking place
To split off a mirrored copy of the /home/xyz file system to new mount point named /jfsstaticcopy, type the following:
chfs -a splitcopy&H3D/jfsstaticcopy /home/xyz
You can control which mirrored copy is used as the backup b using the copy attribute The second mirrored copy is th default if a copy is not specified by the user For example:
chfs -a splitcopy&H3D/jfsstaticcopy -a copy&H3D1 /home/xyz
At this point, a read-only copy of the file system is availabl in /jfsstaticcopy Any changes made to the original file syste after the copy is split off are not reflected in the backu copy
To reintegrate the JFS split image as a mirrored copy at th /testcopy mount point, use the following command:
rmfs /testcopy
The rmfs command removes the file system copy from its split-of state and allows it to be reintegrated as a mirrored copy
Make and Back Up a Snapshot of a JFS2
Beginning with AIX 52, you can make a snapshot of a mounted JFS that establishes a consistent block-level image of the fil system at a point in time The snapshot image remains stabl even as the file system that was used to create the snapshot called the snappedFS, continues to change The snapshot retain the same security permissions as the snappedFS had when th snapshot was made
In the following scenario, you create a snapshot and back up th snapshot to removable media without unmounting or quiescing th file system, all with one command: backsnap You can also us the snapshot for other purposes, such as accessing the files o directories as they existed when the snapshot was taken You ca do the various snapshot procedures using Web-based Syste Manager, SMIT, or the backsnap and snapshot commands
To create a snapshot of the /home/abc/test file system and bac it up (by name) to the tape device /dev/rmt0, use the followin command:
backsnap -m /tmp/snapshot -s size&H3D16M -i f/dev/rmt /home/abc/test
This command creates a logical volume of 16 megabytes for th snapshot of the JFS2 file system (/home/abc/test) The snapsho is mounted on /tmp/snapshot and then a backup by name of th snapshot is made to the tape device After the backup completes the snapshot remains mounted Use the -R flag with the backsna command if you want the snapshot removed when the backu completes
"

Syntax of backnap command:

backsnap&H09Creates and backs up a JFS2 snapshot
backsnap -m /tmp/snapshot/data -s size&H3D16M -i -f /dev/rmt0 /dat : creates a 16 MB LV, creates a snapshot for the /data fil system on the created LV, mounts the snapshot o /tmp/snapshot/data and backups the files and directories in tha file system by name to /dev/rmt0

So, you can create a point in time copy of any given open Fil System of JFS2 type and move to a tape device You can als leave the copy in the snapshot file and the using a script wit cdcreate you can move the contens to a CD or DVD

Do you want to copy RDBMS files ??

Vendors Mentioned
IBM Operating Systems, IBM Security,

Snapshot in AIX 5.2 - Dev Archives

Beginning with AIX 5.2, you can make a snapshot of a mounted JFS2 that establishes a consistent block-level image of the file system at a point in time. The snapshot image remains stable even as the file system that was used to create the snapshot, called the snappedFS, continues to change. The snapshot retains the same security permissions as the snappedFS had when the snapshot was made.

In the following scenario, you create a snapshot and back up the snapshot to removable media without unmounting or quiescing the file system, all with one command: backsnap. You can also use the snapshot for other purposes, such as accessing the files or directories as they existed when the snapshot was taken. You can do the various snapshot procedures using Web-based System Manager, SMIT, or the backsnap and snapshot commands.

To create a snapshot of the /home/abc/test file system and back it up (by name) to the tape device /dev/rmt0, use the following command:

backsnap -m /tmp/snapshot -s size=16M -i f/dev/rmt0 /home/abc/test

This command creates a logical volume of 16 megabytes for the snapshot of the JFS2 file system (/home/abc/test). The snapshot is mounted on /tmp/snapshot and then a backup by name of the snapshot is made to the tape device. After the backup completes, the snapshot remains mounted. Use the -R flag with the backsnap command if you want the snapshot removed when the backup completes.

Another way to do the same:

snapshot Modifies, creates or queries properties a JFS2 snapshot (a consistent block level image of a file system). The bos.rte.file fileset must be installed.

snapshot -o snapfrom=/data /dev/snapsb : creates a snapshot for the /data file system on the exisiting /dev/snapsb LV.
snapshot -d /dev/snapsb : deletes the snapshot and the LV containing the snapshot.

Uses:

Split mirror copy.

backup or snapshot backups in a given point of time performed by the S, not by the application.
In a given Geografical Mirror enviroment you can use snapshots to copy data between the remote nodes.

how to use jfs2 snapshots- - Toolbox for IT Groups

Hi
I'm trying for several days to use jfs2 snapshot but i
just don't manage to do :(
Here what I have to do (automatic everynight in
crontab) :

stop database
snapshot /db/data (jfs2 fs in datavg)
snapshot /db/data/files (jfs2 fs in datavg)
snapshot /db/data/files/index (jfs2 fs in datavg)
start database
mount snapshot fs
backup snapshot fs with networker

I'm using AIX 5.2 ML03.
I have a specific disk (hdisk5) which belong to datavg
and I want to use it for snapshots.

Please can you help? I just can't find how to do.
Thank you very much
kat

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Last modified: March 12, 2019