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https://github.com/ceph/ceph
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Signed-off-by: Sage Weil <sage.weil@dreamhost.com> Reviewed-by: Mark Kampe <mark.kampe@dreamhost.com>
138 lines
5.6 KiB
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138 lines
5.6 KiB
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=================
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Welcome to Ceph
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=================
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Ceph is a unified, distributed storage system that operates on a large
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number of hosts connected by a TCP/IP network. Ceph has been designed
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to accommodate multiple petabytes of storage with ease.
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Ceph Distributed File System provides POSIX filesystem semantics with
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distributed metadata management.
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RADOS is a reliable object store, used by Ceph, but also directly
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accessible by client applications.
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``radosgw`` is an S3-compatible RESTful HTTP service for object
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storage, using RADOS storage.
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RBD is a Linux kernel feature that exposes RADOS storage as a block
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device. Qemu/KVM also has a direct RBD client, that avoids the kernel
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overhead.
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.. ditaa::
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/---------+-----------+-----------\/----------+------\/---------\/-----------\
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| ceph.ko | ceph-fuse | libcephfs || kernel | Qemu || ||librados |
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|c9EE |c3EA |c6F6 || /dev/rbd | /KVM || ||c6F6 |
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+---------+-----------+-----------+|c9EE |c3EA || |+-----------+
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| Ceph DFS (protocol) |+----------+------+| radosgw || |
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| +-----------------+| || || |
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| | ceph-mds || RBD (protocol) || || |
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| |cFA2 || ||cFB5 || |
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+---------------+-----------------++-----------------++---------++ |
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| +=------+ +=------+ |
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| |cls_rbd| |cls_rgw| |
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| +-------+ +-------+ |
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| ceph-osd |
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|cFB3 |
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\----------------------------------------------------------------------------/
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Mailing lists, bug tracker, IRC channel
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=======================================
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- `Ceph Blog <http://ceph.newdream.net/news/>`__: news and status info
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- The development mailing list is at ceph-devel@vger.kernel.org, and
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archived at Gmane_. Send email to subscribe_ or unsubscribe_.
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- `Bug/feature tracker <http://tracker.newdream.net/projects/ceph>`__:
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for filing bugs and feature requests.
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- IRC channel ``#ceph`` on ``irc.oftc.net``: Many of the core
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developers are on IRC, especially daytime in the US/Pacific
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timezone. You are welcome to join and ask questions. You can find
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logs of the channel `here <http://irclogs.ceph.widodh.nl/>`__.
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- `Commercial support <http://ceph.newdream.net/support/>`__
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.. _subscribe: mailto:majordomo@vger.kernel.org?body=subscribe+ceph-devel
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.. _unsubscribe: mailto:majordomo@vger.kernel.org?body=unsubscribe+ceph-devel
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.. _Gmane: http://news.gmane.org/gmane.comp.file-systems.ceph.devel
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Status
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======
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The Ceph project is currently focused on stability. The object store
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(RADOS), radosgw, and RBD are considered reasonably stable. However,
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we do not yet recommend storing valuable data with it yet without
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proper precautions.
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The OSD component of RADOS relies heavily on the stability and
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performance of the underlying filesystem. In the long-term we believe
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that the best performance and stability will come from ``btrfs``.
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Currently, you need to run the latest ``btrfs`` kernel to get the
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latest stability fixes, and there are several performance fixes that
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have not yet hit the mainline kernel. In the short term you may wish
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to carefully consider the tradeoffs between ``xfs``, ``ext4`` and
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``btrfs``. In particular:
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* ``btrfs`` can efficiently clone objects, which improves performance
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and space utilization when using snapshots with RBD and the
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distributed filesystem. ``xfs`` and ``ext4`` will have to copy
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snapshotted objects the first time they are touched.
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* ``xfs`` has a 64 KB limit on extended attributes (xattrs).
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* ``ext4`` has a 4 KB limit on xattrs.
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Ceph uses xattrs for internal object state, snapshot metadata, and
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``radosgw`` ACLs. For most purposes, the 64 KB provided by ``xfs`` is
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plenty, making that our second choice if ``btrfs`` is not an option
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for you. The 4 KB limit in ``ext4`` is easily hit by ``radosgw``, and
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will cause ``ceph-osd`` to crash, making that a poor choice for
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``radosgw`` users. On the other hand, if you are using RADOS or RBD
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without snapshots and without ``radosgw``, ``ext4`` will be just
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fine. We will have a workaround for xattr size limitations shortly,
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making these problems largely go away.
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.. _cfuse-kernel-tradeoff:
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The Ceph filesystem is functionally fairly complete, but has not been
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tested well enough at scale and under load yet. Multi-master MDS is
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still problematic and we recommend running just one active MDS
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(standbys are ok). If you have problems with ``kclient`` or
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``ceph-fuse``, you may wish to try the other option; in general,
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``kclient`` is expected to be faster (but be sure to use the latest
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Linux kernel!) while ``ceph-fuse`` provides better stability by not
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triggering kernel crashes.
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Ceph is developed on Linux. Other platforms may work, but are not the
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focus of the project. Filesystem access from other operating systems
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can be done via NFS or Samba re-exports.
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Table of Contents
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=================
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.. toctree::
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:maxdepth: 3
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start/index
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architecture
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ops/index
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rec/index
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config
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control
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api/index
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Internals <dev/index>
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man/index
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papers
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appendix/index
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Indices and tables
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==================
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- :ref:`genindex`
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