实验性功能¶

CephFS includes a number of experimental features which are not fully stabilized or qualified for users to turn on in real deployments. We generally do our best to clearly demarcate these and fence them off so they can’t be used by mistake.

Some of these features are closer to being done than others, though. We describe each of them with an approximation of how risky they are and briefly describe what is required to enable them. Note that doing so will irrevocably flag maps in the monitor as having once enabled this flag to improve debugging and support processes.

内联数据¶

By default, all CephFS file data is stored in RADOS objects. The inline data feature enables small files (generally <2KB) to be stored in the inode and served out of the MDS. This may improve small-file performance but increases load on the MDS. It is not sufficiently tested to support at this time, although failures within it are unlikely to make non-inlined data inaccessible

Inline data has always been off by default and requires setting the “inline_data” flag.

Mantle: 可编程的元数据负载均衡器¶

Mantle is a programmable metadata balancer built into the MDS. The idea is to protect the mechanisms for balancing load (migration, replication, fragmentation) but stub out the balancing policies using Lua. For details, see Mantle.

快照¶

Like multiple active MDSes, CephFS is designed from the ground up to support snapshotting of arbitrary directories. There are no known bugs at the time of writing, but there is insufficient testing to provide stability guarantees and every expansion of testing has generally revealed new issues. If you do enable snapshots and experience failure, manual intervention will be needed.

Snapshots are known not to work properly with multiple filesystems (below) in some cases. Specifically, if you share a pool for multiple FSes and delete a snapshot in one FS, expect to lose snapshotted file data in any other FS using snapshots. See the CephFS 快照 page for more information.

出于某些含糊的实现原因，内核客户端仅支持最多 400 个快照（ http://tracker.ceph.com/issues/21420 ）。

在 Mimic 版之前，快照功能是用 allow_new_snaps 标记屏蔽的。

单个 Ceph 集群内建多个文件系统¶

Code was merged prior to the Jewel release which enables administrators to create multiple independent CephFS filesystems within a single Ceph cluster. These independent filesystems have their own set of active MDSes, cluster maps, and data. But the feature required extensive changes to data structures which are not yet fully qualified, and has security implications which are not all apparent nor resolved.

There are no known bugs, but any failures which do result from having multiple active filesystems in your cluster will require manual intervention and, so far, will not have been experienced by anybody else – knowledgeable help will be extremely limited. You also probably do not have the security or isolation guarantees you want or think you have upon doing so.

Note that snapshots and multiple filesystems are not tested in combination and may not work together; see above.

Multiple filesystems were available starting in the Jewel release candidates but must be turned on via the enable_multiple flag until declared stable.

LazyIO¶

LazyIO 放松了 POSIX 语义的要求，允许读、写缓冲的存在，即使有多个客户端上的多个应用程序同时打开一个文件时也允许。应用程序自行负责缓存一致性的管理。

曾经是实验性的功能¶

目录分片¶

在 Luminous (12.2.x) 版以前，目录分片功能是实验性的，现在会给新文件系统默认启用。旧版 Ceph 上的文件系统若要启用目录分片功能，可给此文件系统设置 allow_dirfrags 标记。

ceph fs set <filesystem name> allow_dirfrags 1

多活元数据服务器¶

在 Luminous 12.2.x 版之前，在单个文件系统内运行多活元数据服务器是实验性的功能；现在，默认就允许在新文件系统上创建多活元数据服务器。

用较老版本的 Ceph 创建的文件系统仍然需要明确启用多活元数据服务器，如下：

ceph fs set <file system name> allow_multimds 1

注意，活跃 MDS 集群的默认尺寸（ max_mds ），其初始值仍然是 1 。