--- /dev/null
- Specify the maximum write size in bytes. Default: 16 MB.
+.. SPDX-License-Identifier: GPL-2.0
+
+============================
+Ceph Distributed File System
+============================
+
+Ceph is a distributed network file system designed to provide good
+performance, reliability, and scalability.
+
+Basic features include:
+
+ * POSIX semantics
+ * Seamless scaling from 1 to many thousands of nodes
+ * High availability and reliability. No single point of failure.
+ * N-way replication of data across storage nodes
+ * Fast recovery from node failures
+ * Automatic rebalancing of data on node addition/removal
+ * Easy deployment: most FS components are userspace daemons
+
+Also,
+
+ * Flexible snapshots (on any directory)
+ * Recursive accounting (nested files, directories, bytes)
+
+In contrast to cluster filesystems like GFS, OCFS2, and GPFS that rely
+on symmetric access by all clients to shared block devices, Ceph
+separates data and metadata management into independent server
+clusters, similar to Lustre. Unlike Lustre, however, metadata and
+storage nodes run entirely as user space daemons. File data is striped
+across storage nodes in large chunks to distribute workload and
+facilitate high throughputs. When storage nodes fail, data is
+re-replicated in a distributed fashion by the storage nodes themselves
+(with some minimal coordination from a cluster monitor), making the
+system extremely efficient and scalable.
+
+Metadata servers effectively form a large, consistent, distributed
+in-memory cache above the file namespace that is extremely scalable,
+dynamically redistributes metadata in response to workload changes,
+and can tolerate arbitrary (well, non-Byzantine) node failures. The
+metadata server takes a somewhat unconventional approach to metadata
+storage to significantly improve performance for common workloads. In
+particular, inodes with only a single link are embedded in
+directories, allowing entire directories of dentries and inodes to be
+loaded into its cache with a single I/O operation. The contents of
+extremely large directories can be fragmented and managed by
+independent metadata servers, allowing scalable concurrent access.
+
+The system offers automatic data rebalancing/migration when scaling
+from a small cluster of just a few nodes to many hundreds, without
+requiring an administrator carve the data set into static volumes or
+go through the tedious process of migrating data between servers.
+When the file system approaches full, new nodes can be easily added
+and things will "just work."
+
+Ceph includes flexible snapshot mechanism that allows a user to create
+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'.
+
+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
+subdirectories, and a summation of all nested file sizes. This makes
+the identification of large disk space consumers relatively quick, as
+no 'du' or similar recursive scan of the file system is required.
+
+Finally, Ceph also allows quotas to be set on any directory in the system.
+The quota can restrict the number of bytes or the number of files stored
+beneath that point in the directory hierarchy. Quotas can be set using
+extended attributes 'ceph.quota.max_files' and 'ceph.quota.max_bytes', eg::
+
+ setfattr -n ceph.quota.max_bytes -v 100000000 /some/dir
+ getfattr -n ceph.quota.max_bytes /some/dir
+
+A limitation of the current quotas implementation is that it relies on the
+cooperation of the client mounting the file system to stop writers when a
+limit is reached. A modified or adversarial client cannot be prevented
+from writing as much data as it needs.
+
+Mount Syntax
+============
+
+The basic mount syntax is::
+
+ # mount -t ceph monip[:port][,monip2[:port]...]:/[subdir] mnt
+
+You only need to specify a single monitor, as the client will get the
+full list when it connects. (However, if the monitor you specify
+happens to be down, the mount won't succeed.) The port can be left
+off if the monitor is using the default. So if the monitor is at
+1.2.3.4::
+
+ # mount -t ceph 1.2.3.4:/ /mnt/ceph
+
+is sufficient. If /sbin/mount.ceph is installed, a hostname can be
+used instead of an IP address.
+
+
+
+Mount Options
+=============
+
+ ip=A.B.C.D[:N]
+ Specify the IP and/or port the client should bind to locally.
+ There is normally not much reason to do this. If the IP is not
+ specified, the client's IP address is determined by looking at the
+ address its connection to the monitor originates from.
+
+ wsize=X
- Specify the maximum read size in bytes. Default: 16 MB.
++ Specify the maximum write size in bytes. Default: 64 MB.
+
+ rsize=X
- of a non-responsive Ceph file system. The default is 30
++ Specify the maximum read size in bytes. Default: 64 MB.
+
+ rasize=X
+ Specify the maximum readahead size in bytes. Default: 8 MB.
+
+ mount_timeout=X
+ Specify the timeout value for mount (in seconds), in the case
++ of a non-responsive Ceph file system. The default is 60
+ seconds.
+
+ caps_max=X
+ Specify the maximum number of caps to hold. Unused caps are released
+ when number of caps exceeds the limit. The default is 0 (no limit)
+
+ rbytes
+ When stat() is called on a directory, set st_size to 'rbytes',
+ the summation of file sizes over all files nested beneath that
+ directory. This is the default.
+
+ norbytes
+ When stat() is called on a directory, set st_size to the
+ number of entries in that directory.
+
+ nocrc
+ Disable CRC32C calculation for data writes. If set, the storage node
+ must rely on TCP's error correction to detect data corruption
+ in the data payload.
+
+ dcache
+ Use the dcache contents to perform negative lookups and
+ readdir when the client has the entire directory contents in
+ its cache. (This does not change correctness; the client uses
+ cached metadata only when a lease or capability ensures it is
+ valid.)
+
+ nodcache
+ Do not use the dcache as above. This avoids a significant amount of
+ complex code, sacrificing performance without affecting correctness,
+ and is useful for tracking down bugs.
+
+ noasyncreaddir
+ Do not use the dcache as above for readdir.
+
+ noquotadf
+ Report overall filesystem usage in statfs instead of using the root
+ directory quota.
+
+ nocopyfrom
+ Don't use the RADOS 'copy-from' operation to perform remote object
+ copies. Currently, it's only used in copy_file_range, which will revert
+ to the default VFS implementation if this option is used.
+
+ recover_session=<no|clean>
+ Set auto reconnect mode in the case where the client is blacklisted. The
+ available modes are "no" and "clean". The default is "no".
+
+ * no: never attempt to reconnect when client detects that it has been
+ blacklisted. Operations will generally fail after being blacklisted.
+
+ * clean: client reconnects to the ceph cluster automatically when it
+ detects that it has been blacklisted. During reconnect, client drops
+ dirty data/metadata, invalidates page caches and writable file handles.
+ After reconnect, file locks become stale because the MDS loses track
+ of them. If an inode contains any stale file locks, read/write on the
+ inode is not allowed until applications release all stale file locks.
+
+More Information
+================
+
+For more information on Ceph, see the home page at
+ https://ceph.com/
+
+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
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