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-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. 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
-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 write size in bytes. By default there is no
- maximum. 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 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.
-
-More Information
-================
-
-For more information on Ceph, see the home page at
- http://ceph.newdream.net/
-
-The Linux kernel client source tree is available at
- git://ceph.newdream.net/git/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
- git://ceph.newdream.net/git/ceph.git