From: Ken Dreyer Date: Thu, 25 May 2017 03:51:54 +0000 (-0600) Subject: doc: describe CephFS max_file_size X-Git-Tag: v12.1.0~57^2~32^2~1 X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=02753cdb9184215e812d126a7103ecf9a72cfcee;p=ceph.git doc: describe CephFS max_file_size Add a description of max_file_size to the CephFS admin docs. Thanks to John Spray on ceph-users for this information. Signed-off-by: Ken Dreyer --- diff --git a/doc/cephfs/administration.rst b/doc/cephfs/administration.rst index 7375a7618e45..ccf6263d641c 100644 --- a/doc/cephfs/administration.rst +++ b/doc/cephfs/administration.rst @@ -42,6 +42,38 @@ creation of multiple filesystems use ``ceph fs flag set enable_multiple true``. fs rm_data_pool +Settings +-------- + +:: + + fs set max_file_size + +CephFS has a configurable maximum file size, and it's 1TB by default. +You may wish to set this limit higher if you expect to store large files +in CephFS. It is a 64-bit field. + +Setting ``max_file_size`` to 0 does not disable the limit. It would +simply limit clients to only creating empty files. + + +Maximum file sizes and performance +---------------------------------- + +CephFS enforces the maximum file size limit at the point of appending to +files or setting their size. It does not affect how anything is stored. + +When users create a file of an enormous size (without necessarily +writing any data to it), some operations (such as deletes) cause the MDS +to have to do a large number of operations to check if any of the RADOS +objects within the range that could exist (according to the file size) +really existed. + +The ``max_file_size`` setting prevents users from creating files that +appear to be eg. exabytes in size, causing load on the MDS as it tries +to enumerate the objects during operations like stats or deletes. + + Daemons -------