2012-05-18 20:54:51 +00:00
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============
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Filesystem
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============
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For details on file systems when configuring a cluster See
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`Hard Disk and File System Recommendations`_ .
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.. tip:: We recommend configuring Ceph to use the ``XFS`` file system in
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the near term, and ``btrfs`` in the long term once it is stable
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enough for production.
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Before ``ext3``, ``ReiserFS`` was the only journaling file system available for
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Linux. However, ``ext3`` doesn't provide Extended Attribute (XATTR) support.
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While ``ext4`` provides XATTR support, it only allows XATTRs up to 4kb. The
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4kb limit is not enough for RADOS GW ACLs, snapshots, and other features. As of
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version 0.45, Ceph provides a ``leveldb`` feature for ``ext4`` file systems
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that stores XATTRs in excess of 4kb in a ``leveldb`` database.
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The ``XFS`` and ``btrfs`` file systems provide numerous advantages in highly
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scaled data storage environments when `compared`_ to ``ext3`` and ``ext4``.
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Both ``XFS`` and ``btrfs`` are `journaling file systems`_, which means that
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they are more robust when recovering from crashes, power outages, etc. These
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filesystems journal all of the changes they will make before performing writes.
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``XFS`` was developed for Silicon Graphics, and is a mature and stable
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filesystem. By contrast, ``btrfs`` is a relatively new file system that aims
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to address the long-standing wishes of system administrators working with
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large scale data storage environments. ``btrfs`` has some unique features
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and advantages compared to other Linux filesystems.
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``btrfs`` is a `copy-on-write`_ filesystem. It supports file creation
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timestamps and checksums that verify metadata integrity, so it can detect
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bad copies of data and fix them with the good copies. The copy-on-write
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capability means that ``btrfs`` can support snapshots that are writable.
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``btrfs`` supports transparent compression and other features.
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``btrfs`` also incorporates multi-device management into the file system,
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which enables you to support heterogeneous disk storage infrastructure,
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data allocation policies. The community also aims to provide ``fsck``,
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deduplication, and data encryption support in the future. This compelling
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list of features makes ``btrfs`` the ideal choice for Ceph clusters.
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.. _copy-on-write: http://en.wikipedia.org/wiki/Copy-on-write
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.. _Hard Disk and File System Recommendations: ../../config-cluster/file-system-recommendations
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.. _compared: http://en.wikipedia.org/wiki/Comparison_of_file_systems
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.. _journaling file systems: http://en.wikipedia.org/wiki/Journaling_file_system
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