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-rw-r--r--Documentation/filesystems/ceph.rst11
1 files changed, 10 insertions, 1 deletions
diff --git a/Documentation/filesystems/ceph.rst b/Documentation/filesystems/ceph.rst
index 4942e018db85..085f309ece60 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
@@ -203,7 +213,6 @@ For more information on Ceph, see the home page at
The Linux kernel client source tree is available at
- https://github.com/ceph/ceph-client.git
- - git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client.git
and the source for the full system is at
https://github.com/ceph/ceph.git