It may happen sometimes to get the error message "mkvgdata ATTENTION: The type of the logical volume /dev/lv_XXX does not match with filesystem's type." when trying to create a mksysb image:

Full error here:

0042-001 nim: processing error encountered on "master":
       0042-001 m_mkbosi: processing error encountered on "gznimclient":
       
    mkvgdata ATTENTION: The type of the logical volume /dev/lv_XXX does not match 
    with filesystem's type.
    
    
    ----------+
    
    Required = 10324384 (10083 MB)    Available = 616420296 (601973 MB)
    
    
    
    Creating information file (/image.data) for rootvg.
    0512-008 savevg: The mkvgdata command failed.  Backup canceled.

This is because, in this example, the lv type is jfs2 and filesystem type jfs:

gznimclient:root:/home/root # lslv lv_XXX
LOGICAL VOLUME:     lv_XXX        VOLUME GROUP:   rootvg
LV IDENTIFIER:      00c800ee00004c0000000122b66dfebe.20 PERMISSION:     read/write
VG STATE:           active/complete        LV STATE:       opened/syncd
[color=red]TYPE:               jfs2[/color]                   WRITE VERIFY:   off
MAX LPs:            512                    PP SIZE:        128 megabyte(s)
COPIES:             1                      SCHED POLICY:   parallel
LPs:                1                      PPs:            1
STALE PPs:          0                      BB POLICY:      relocatable
INTER-POLICY:       minimum                RELOCATABLE:    yes
INTRA-POLICY:       middle                 UPPER BOUND:    32
MOUNT POINT:        /opt/event_routeur     LABEL:          /opt/event_routeur
MIRROR WRITE CONSISTENCY: on/ACTIVE                              
EACH LP COPY ON A SEPARATE PV ?: yes                                    
Serialize IO ?:     NO                                     
gznimclient:root:/home/root # mount|grep lv_XXX
         /dev/lv_XXX /opt/event_routeur [color=red]jfs[/color]    Feb 12 09:17 rw,nosuid,log=/dev/loglv01

Now, you basically have two possibilities: modify the lv or the filesystem.

Obviously, if you touch the filesystem, you need to move the data, reformat it and put the data back. Heavy, right?
So the best way is to modify the lv. The solution is pretty simple and it involves the chlv command:

gznimclient:root:/home/root # [color=blue]chlv -t jfs lv_XXX[/color]
gznimclient:root:/home/root # lslv lv_XXX
LOGICAL VOLUME:     lv_XXX        VOLUME GROUP:   rootvg
LV IDENTIFIER:      00c800ee00004c0000000122b66dfebe.20 PERMISSION:     read/write
VG STATE:           active/complete        LV STATE:       opened/syncd
[color=green]TYPE:               jfs[/color]                    WRITE VERIFY:   off
MAX LPs:            512                    PP SIZE:        128 megabyte(s)
COPIES:             1                      SCHED POLICY:   parallel
LPs:                1                      PPs:            1
STALE PPs:          0                      BB POLICY:      relocatable
INTER-POLICY:       minimum                RELOCATABLE:    yes
INTRA-POLICY:       middle                 UPPER BOUND:    32
MOUNT POINT:        /opt/event_routeur     LABEL:          /opt/event_routeur
MIRROR WRITE CONSISTENCY: on/ACTIVE                              
EACH LP COPY ON A SEPARATE PV ?: yes                                    
Serialize IO ?:     NO

Well done, you are head of the class now! :)