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    Subject[PATCH 01/19] ceph: documentation
    Mount options, syntax.

    Signed-off-by: Sage Weil <>
    Documentation/filesystems/ceph.txt | 140 ++++++++++++++++++++++++++++++++++++
    1 files changed, 140 insertions(+), 0 deletions(-)
    create mode 100644 Documentation/filesystems/ceph.txt

    diff --git a/Documentation/filesystems/ceph.txt b/Documentation/filesystems/ceph.txt
    new file mode 100644
    index 0000000..66e40e4
    --- /dev/null
    +++ b/Documentation/filesystems/ceph.txt
    @@ -0,0 +1,140 @@
    +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 points 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
    + * 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. Storage nodes
    +utilize btrfs to store data objects, leveraging its advanced features
    +(checksumming, metadata replication, etc.). 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.
    +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
    + # mount -t ceph /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]
    + port=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 it's connection to the monitor originates from.
    + wsize=X
    + Specify the maximum write size in bytes. By default there is no
    + maximu. Ceph will normally size writes based on the file stripe
    + size.
    + rsize=X
    + Specify the maximum readahead.
    + mount_timeout=X
    + Specify the timeout value for mount (in seconds), in the case
    + of a non-responsive Ceph file system. The default is 30
    + seconds.
    + 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 OSD
    + must rely on TCP's error correction to detect data corruption
    + in the data payload.
    + noasyncreaddir
    + Disable client's use its local cache to satisfy readdir
    + requests. (This does not change correctness; the client uses
    + cached metadata only when a lease or capability ensures it is
    + valid.)
    +More Information
    +For more information on Ceph, see the home page at
    +The Linux kernel client source tree is available at
    + git://
    +and the source for the full system is at
    + git://

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