Technology Level 3, Service Pack 1 for AIX 7.1 introduced a new feature for the mksysb utility. This new feature makes it possible to create consistent mksysb backups of your AIX systems using file system snapshot technology. This feature is also available with Technology Level 9 for AIX 6.1.
Previously, when taking a mksysb image of an AIX system, the administrator would often see messages stating the files that were meant to be backed up were now missing (usually transient temporary files) or occasionally there would be issues backing up files that were currently “in use”. Often the administrator would need to quiesce the system in order to take a “clean” backup of the system. And, depending on the size of the system, the time required to perform the backup (with the system offline) was significant.
A solution was required to provide the administrator with the ability to create a volume group backup without having to quiesce the system (or volume group). This would allow the backup to complete (without missing any files) and provide a consistent and functionally stable backup.
This challenge is easily answered using the file system snapshot technology already built-in to AIX. JFS2 has the ability to create snapshots of a mounted JFS2 file system. This creates a consistent (block-level) image of the file system at a point in time.
The mksysb command has been enhanced to call the snapshot command to create snapshots of the JFS2 file systems (in rootvg) and then use the snapshots to create a mksysb backup. To enable the snapshot feature, use the new –T flag with the mksysb command.
Not surprisingly, a few other AIX ‘backup related’ commands have also benefited from this new feature. The savevg, savewpar, mkcd and mkdvd commands have all been enhanced to accept the new –T flag to enable file system snapshots.
The mksysb snapshot feature creates an external snapshot of each of the mounted JFS2 file systems in the root volume group. This requires additional free space in the volume group to create the external logical volumes for each snapshot file system. When the backup is complete, the snapshots are deleted.
Note: snapshots are only available for JFS2 file systems. JFS file systems in a volume group will be backed up using traditional methods.
Here’s an example of using the –T flag with the mksysb command.
After issuing the mksysb command we soon see the message “Creating snapshots”.
# oslevel -s
7100-03-01-1341
# mksysb -Tvie /mksysb/lpar11-mksysb-snapshot
mksysb -Tvie /mksysb/lpar11-mksysb-snapshot
Creating information file (/image.data) for rootvg.
Creating snapshots.
…
Looking at the output from the df command, we observe several snapshot file systems have been created and mounted.
# df
Filesystem 512-blocks Free %Used Iused %Iused Mounted on
/dev/hd4 2097152 1694480 20% 11782 6% /
/dev/hd2 8388608 4077360 52% 52184 11% /usr
/dev/hd9var 4194304 3614496 14% 6458 2% /var
/dev/hd3 2097152 2086056 1% 69 1% /tmp
/dev/hd1 131072 130360 1% 5 1% /home
/dev/hd11admin 262144 261384 1% 10 1% /admin
/proc - - - - - /proc
/dev/hd10opt 2097152 1702160 19% 6991 4% /opt
/dev/livedump 524288 523552 1% 4 1% /var/adm/ras/livedump
/dev/fixeslv 13107200 2050688 85% 1463 1% /fixes
/aha - - - 18 1% /aha
/dev/mksysblv 13107200 13104544 1% 4 1% /mksysb
/dev/fslv00 131072 124416 6% - - /admin/mksysb.7471128
/dev/fslv01 655360 654336 1% - - /admin/mksysb.7471128/usr
/dev/fslv02 131072 129792 1% - - /admin/mksysb.7471128/var
/dev/fslv03 131072 130304 1% - - /admin/mksysb.7471128/tmp
/dev/fslv04 131072 130304 1% - - /admin/mksysb.7471128/home
/dev/fslv05 131072 130304 1% - - /admin/mksysb.7471128/opt
/dev/fslv06 131072 130304 1% - - /admin/mksysb.7471128/admin
/dev/fslv07 131072 130304 1% - - /admin/mksysb.7471128/var/adm/ras/livedump
/dev/fslv08 1703936 1702400 1% - - /admin/mksysb.7471128/fixes
/dev/fslv09 131072 130304 1% - - /admin/mksysb.7471128/mksysb
And we see the corresponding snapshot logical volumes in the root volume group.
# lsvg -l rootvg
rootvg:
LV NAME TYPE LPs PPs PVs LV STATE MOUNT POINT
hd5 boot 1 1 1 closed/syncd N/A
hd6 paging 8 8 1 open/syncd N/A
hd8 jfs2log 1 1 1 open/syncd N/A
hd4 jfs2 16 16 1 open/syncd /
hd2 jfs2 64 64 1 open/syncd /usr
hd9var jfs2 32 32 1 open/syncd /var
hd3 jfs2 16 16 1 open/syncd /tmp
hd1 jfs2 1 1 1 open/syncd /home
hd10opt jfs2 16 16 1 open/syncd /opt
hd11admin jfs2 2 2 1 open/syncd /admin
lg_dumplv sysdump 16 16 1 open/syncd N/A
livedump jfs2 4 4 1 open/syncd /var/adm/ras/livedump
fixeslv jfs2 100 100 1 open/syncd /fixes
mksysblv jfs2 100 100 1 open/syncd /mksysb
fslv00 jfs2 1 1 1 open/syncd N/A
fslv01 jfs2 5 5 1 open/syncd N/A
fslv02 jfs2 1 1 1 open/syncd N/A
fslv03 jfs2 1 1 1 open/syncd N/A
fslv04 jfs2 1 1 1 open/syncd N/A
fslv05 jfs2 1 1 1 open/syncd N/A
fslv06 jfs2 1 1 1 open/syncd N/A
fslv07 jfs2 1 1 1 open/syncd N/A
fslv08 jfs2 13 13 1 open/syncd N/A
fslv09 jfs2 1 1 1 open/syncd N/A
Whilst the mksysb backup is still running, we are able to query the status of each snapshot using the snapshot command.
# snapshot -q /
Snapshots for /
Current Location 512-blocks Free Time
* /dev/fslv00 131072 123392 Mon Dec 2 12:57:11 2013
Snapshots for /
Current Location 512-blocks Free Time
* /dev/fslv00 131072 123392 Mon Dec 2 12:57:11 2013
Snapshots for /usr
Current Location 512-blocks Free Time
* /dev/fslv01 655360 646656 Mon Dec 2 12:57:13 2013
Snapshots for /var
Current Location 512-blocks Free Time
* /dev/fslv02 131072 129024 Mon Dec 2 12:57:14 2013
Snapshots for /tmp
Current Location 512-blocks Free Time
* /dev/fslv03 131072 130048 Mon Dec 2 12:57:16 2013
Snapshots for /home
Current Location 512-blocks Free Time
* /dev/fslv04 131072 130304 Mon Dec 2 12:57:17 2013
Snapshots for /opt
Current Location 512-blocks Free Time
* /dev/fslv05 131072 129536 Mon Dec 2 12:57:18 2013
Snapshots for /admin
Current Location 512-blocks Free Time
* /dev/fslv06 131072 130304 Mon Dec 2 12:57:20 2013
Snapshots for /var/adm/ras/livedump
Current Location 512-blocks Free Time
* /dev/fslv07 131072 130304 Mon Dec 2 12:57:21 2013
Snapshots for /fixes
Current Location 512-blocks Free Time
* /dev/fslv08 1703936 1701376 Mon Dec 2 12:57:22 2013
Snapshots for /mksysb
Current Location 512-blocks Free Time
* /dev/fslv09 131072 130304 Mon Dec 2 12:57:24 2013
From the mksysb man page:
-T = Creates backup by using snapshots. This command applies only to JFS2 file systems. When you specify the -T flag to use snapshots for creating a volume group backup, external JFS2 snapshots are created. Snapshots allow for a point-in-time image of a JFS2 file system and thus, do not require a system to be put into a temporarily inactive state. The size of the snapshot is 2% - 15% of the size of the file system. The snapshot logical volumes are removed when back up is complete. However, snapshots are not removed if a file system already has other snapshots. Additionally, if a file system has internal snapshots, external snapshots cannot be created and thus, snapshots are not used for creating the backup of the file system. The use of the -T flag does not affect any JFS file systems that are present in the volume group that is being backed up. These file systems are backed up in the same manner as done previously.
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