8136b58dd0
New documentation should have an entry in the 00-INDEX. Correct git urls. Signed-off-by: Cheng Renquan <crquan@gmail.com> Signed-off-by: Sage Weil <sage@newdream.net>
141 lines
5.3 KiB
Plaintext
141 lines
5.3 KiB
Plaintext
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 it's 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.
|
|
|
|
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
|
|
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
|