Signed-off-by: Luís Henriques <[email protected]>
---
Documentation/filesystems/ceph.rst | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/Documentation/filesystems/ceph.rst b/Documentation/filesystems/ceph.rst
index 4942e018db85..d487cabe792d 100644
--- a/Documentation/filesystems/ceph.rst
+++ b/Documentation/filesystems/ceph.rst
@@ -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