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ceph: update documentation regarding snapshot naming limitations 

Signed-off-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Milind Changire <mchangir@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
This commit is contained in:
Luís Henriques 2022-08-25 09:31:30 -04:00 committed by Ilya Dryomov
parent abd4fc7758
commit 230bd8b98d
1 changed files with 10 additions and 0 deletions
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Documentation/filesystems/ceph.rst
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@ -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 system. Snapshot creation and deletion are as simple as 'mkdir
.snap/foo' and 'rmdir .snap/foo'. .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 Ceph also provides some recursive accounting on directories for nested
files and bytes. That is, a 'getfattr -d foo' on any directory in the 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 system will reveal the total number of nested regular files and