vxfs fsadm: attempt to resize......failed with errno 28

When extending the filesystem online using fsadm command its failing with below error:

# fsadm -F vxfs -b 10240M /fs_test 
vxfs fsadm: /dev/vg00/rfstest is currently 5636096 sectors - size will be increased
vxfs fsadm: attempt to resize /dev/vg00/rfstest failed with errno 28 
vxfs fsadm:  Retry the operation after freeing up some space

Error number 28 means ENOSPC from /usr/include/sys/errno.h
#define ENOSPC          28      /* No space left on device      */


Why is the ENOSPC
error while running fsadm even though there is enough free space on the filesystem?
Solution
NOTE: If a file system is full, busy or too fragmented, the resize operation may fails.

Follow the below steps to extend the filesystem online using fsadm :
Checked and found filesystem is heavily fragmented. As it can be seen from the above output that there is no free extent of 8KB or above.

# fsadm -F vxfs -D -E /fs_test 

  Directory Fragmentation Report
             Dirs        Total      Immed    Immeds   Dirs to   Blocks to
             Searched    Blocks     Dirs     to Add   Reduce    Reduce
  total          2887      1996      2131         0         3          99

  Extent Fragmentation Report
        Total    Average      Average     Total
        Files    File Blks    # Extents   Free Blks
        47977          85           5     1513016
    blocks used for indirects: 26820
    % Free blocks in extents smaller than 64 blks: 100.00
    % Free blocks in extents smaller than  8 blks: 100.00
    % blks allocated to extents 64 blks or larger: 90.52
    Free Extents By Size
           1:     215670            2:     221005            4:     213834
           8:          0           16:          0           32:          0
          64:          0          128:          0          256:          0
         512:          0         1024:          0         2048:          0
        4096:          0         8192:          0        16384:          0
       32768:          0        65536:          0       131072:          0
      262144:          0       524288:          0      1048576:          0
     2097152:          0      4194304:          0      8388608:          0
    16777216:          0     33554432:          0     67108864:          0
   134217728:          0    268435456:          0    536870912:          0
  1073741824:          0   2147483648
Ran the defragmentation on the filesystem.

# fsadm -F vxfs -d -e /fs_test 
NOTE: Defragmentation can take long time depending on the degree of fragmentation, disk speed and number of inodes in the filesystem. In this case it took about 45 min. More information is available on man 1M fsadm_vxfs command.
Fragmentation report after defragmentation of filesystem:

# fsadm -F vxfs -D -E /fs_test 

  Directory Fragmentation Report
             Dirs        Total      Immed    Immeds   Dirs to   Blocks to
             Searched    Blocks     Dirs     to Add   Reduce    Reduce
  total          2887      1879      2131         0         2           5

  Extent Fragmentation Report
        Total    Average      Average     Total
        Files    File Blks    # Extents   Free Blks
        47977          84           1     1539889
    blocks used for indirects: 48
    % Free blocks in extents smaller than 64 blks: 4.94
    % Free blocks in extents smaller than  8 blks: 0.52
    % blks allocated to extents 64 blks or larger: 91.40
    Free Extents By Size
           1:       1029            2:       1144            4:       1165
           8:       1319           16:       1253           32:       1170
          64:       1023          128:        879          256:        611
         512:        388         1024:        171         2048:         89
        4096:         36         8192:         12        16384:          4
       32768:          4        65536:          0       131072:          1
      262144:          0       524288:          0      1048576:          0
     2097152:          0      4194304:          0      8388608:          0
    16777216:          0     33554432:          0     67108864:          0
   134217728:          0    268435456:          0    536870912:          0
  1073741824:          0   2147483648:          0
Now its looks much better. Free extents are larger blocks.
Tried extending the filesystem now using fsadm command and its successful now:

# fsadm -F vxfs -b 10485760 /fs_test
UX:vxfs fsadm: INFO: V-3-25942: /dev/vg00/rfstest size increased from 5636096 sectors to 10485760 sectors

# bdf /fs_test 
Filesystem              kbytes    used   avail %used Mounted on
/dev/vg00/fstest      10485760 4097395 5990074   41% /fs_test