Commit 230bd8b9 authored by Luís Henriques's avatar Luís Henriques Committed by Ilya Dryomov
Browse files

ceph: update documentation regarding snapshot naming limitations 



Signed-off-by: default avatarLuís Henriques <lhenriques@suse.de>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Reviewed-by: default avatarXiubo Li <xiubli@redhat.com>
Reviewed-by: default avatarMilind Changire <mchangir@redhat.com>
Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
parent abd4fc77

Documentation/filesystems/ceph.rst

+10 −0
Original line number Diff line number Diff line
@@ -57,6 +57,16 @@ a snapshot on any subdirectory (and its nested contents) in the 
system.  Snapshot creation and deletion are as simple as 'mkdir

.snap/foo' and 'rmdir .snap/foo'.



Snapshot names have two limitations:



* They can not start with an underscore ('_'), as these names are reserved

  for internal usage by the MDS.

* They can not exceed 240 characters in size.  This is because the MDS makes

  use of long snapshot names internally, which follow the format:

  `_<SNAPSHOT-NAME>_<INODE-NUMBER>`.  Since filenames in general can't have

  more than 255 characters, and `<node-id>` takes 13 characters, the long

  snapshot names can take as much as 255 - 1 - 1 - 13 = 240.



Ceph also provides some recursive accounting on directories for nested

files and bytes.  That is, a 'getfattr -d foo' on any directory in the

system will reveal the total number of nested regular files and