xfs_db -r -c "sb 0" -c "p" -c "freesp -s" /dev/sdb1|grep ifree

xfs_db -r -c "sb 0" -c "p" -c "freesp -s " /dev/sdb1

xfsdump -L osd0 -M osd0 -f /mnt/osd0 /var/lib/ceph/osd/ceph-0

[root@lab8107 ceph-0]# xfsrestore -f /mnt/osd0 /var/lib/ceph/osd/ceph-0
xfsrestore: using file dump (drive_simple) strategy
xfsrestore: version 3.1.4 (dump format 3.0) - type ^C for status and control
xfsrestore: ERROR: unable to create /var/lib/ceph/osd/ceph-0/xfsrestorehousekeepingdir: No space left on device
xfsrestore: Restore Status: ERROR

mv /var/lib/ceph/osd/ceph-0/current/ /mnt

xfsrestore  -o -f /mnt/osd0 /var/lib/ceph/osd/ceph-0

systemctl restart ceph-osd@0

[root@lab8107 test]# seq 100|xargs -i dd if=a of=a{} bs=100K count=1

[root@lab8107 test]# seq 100|xargs -i xfs_bmap -v a{} |less

inotifywait -m --timefmt '%Y %B %d %H:%M:%S' --format '%T %w %e %f' -r -m /var/lib/ceph/osd/ceph-0/

for a in `ls ./`;do rados -p rbd put $a $a;done

rados -p rbd bench -b 100K 6000 write --no-cleanup

command_check_call: Running command: /usr/sbin/mkfs -t xfs -f -i size=2048 -- /dev/sdb1

xfs=[
    # xfs insists on not overwriting previous fs; even if we wipe
    # partition table, we often recreate it exactly the same way,
    # so we'll see ghosts of filesystems past
    '-f',
    '-i', 'size=2048',
],

'-i', 'size=256',

[root@lab8107 ~]# uname  -a
Linux lab8107 4.13.0-1.el7.elrepo.x86_64 #1 SMP Sun Sep 3 19:07:24 EDT 2017 x86_64 x86_64 x86_64 GNU/Linux

[root@lab8107 ~]# rpm -qa|grep xfsprogs
xfsprogs-4.12.0-4.el7.centos.x86_64

[root@lab8107 ~]# df -h /var/lib/ceph/osd/ceph-0
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdb1       9.4G  9.0G  395M  96% /var/lib/ceph/osd/ceph-0

meta_uuid = 00000000-0000-0000-0000-000000000000
   from      to extents  blocks    pct
      1       1     545     545   0.50
      2       3     665    1666   1.52
      4       7    1624    8927   8.12
      8      15    1853   19063  17.34
     16      31      19     352   0.32
   4096    8191       1    7694   7.00
  16384   32767       3   71659  65.20
total free extents 4710
total free blocks 109906
average free extent size 23.3346
[root@lab8107 ~]# xfs_db -r -c "sb 0" -c "p" -c "freesp -s " /dev/sdb1

sparse[=value]
  Enable sparse inode chunk allocation. The value is either 0 or 1, with 1 signifying that sparse allocation is enabled.  If  the value  is omitted, 1 is assumed. Sparse inode allocation is disabled by default. This feature is only available for filesystems formatted with -m crc=1.
  
   When enabled, sparse inode allocation allows the filesystem to allocate smaller than the  standard  64-inode  chunk  when  free space  is  severely  limited. This feature is useful for filesystems that might fragment free space over time such that no free extents are large enough to accommodate a chunk of 64 inodes. Without this feature enabled, inode allocations can fail with out of space errors under severe fragmented free space conditions.