0516-404 allocpThis system cannot fulfill the allocation -

While trying to increase space on one of my file systems I get the following error,

Code:

[/home/root] #chfs -a size=+5G /fns/ld/r
0516-404 allocp: This system cannot fulfill the allocation 
                 request. There are not enough free partitions or not 
                 enough physical volumes to keep strictness and satisfy 
                 allocation requests.  The command should be retried with 
                 different allocation characteristics.

I am trying to increase space on,

Code:

[/home/root] #df -gt | grep /fns/l
/dev/fns_l_lv      3.00      1.09      1.91   37% /fns/l/r
/dev/fns_ld_lv      8.00      8.00      0.00  100% /fns/ld/r
/dev/fns_ls_lv      1.00      0.16      0.84   16% /fns/ls/r

The file system as you can see is a mirrored one,

Code:

[/home/root] #lsvg -l fnsvg | grep /fns/l
fns_l_lv            jfs2       24    48    2    open/syncd    /fns/l/r
fns_ld_lv           jfs2       64    128   2    open/syncd    /fns/ld/r
fns_ls_lv           jfs2       8     16    2    open/syncd    /fns/ls/r

There are two disks in this mirrored relationship,

Code:

lspv
hdisk0        000030d7b108e3f4                    fnsvg           active
hdisk1        000030d7b108ea78                    fnsvg           active
hdisk2        000030d7b9285c69                    rootvg          active
hdisk3        000030d7b8c88a41                    rootvg          active

And when I checked, one of the disks was almost out of space,

Code:

[/home/root] #lspv hdisk0
PHYSICAL VOLUME:    hdisk0                   VOLUME GROUP:     fnsvg
PV IDENTIFIER:      000030d7b108e3f4 VG IDENTIFIER     000030d70000d60000000111b108f477
PV STATE:           active                                     
STALE PARTITIONS:   0                        ALLOCATABLE:      yes
PP SIZE:            128 megabyte(s)          LOGICAL VOLUMES:  46
TOTAL PPs:          2235 (286080 megabytes)  VG DESCRIPTORS:   2
FREE PPs:           2 (256 megabytes)        HOT SPARE:        no
USED PPs:           2233 (285824 megabytes)  MAX REQUEST:      256 kilobytes
FREE DISTRIBUTION:  00..00..00..00..02                         
USED DISTRIBUTION:  447..447..447..447..445

Now what I don't understand here is, if it is a mirrored pair, why is the space consumed more from one disk than the other? Shouldn't they be equally consumed?