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ceph: update documentation regarding snapshot naming limitations

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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>
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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
.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