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Signed-off-by: John Wilkins <john.wilkins@dreamhost.com> Signed-off-by: Tommi Virtanen <tommi.virtanen@dreamhost.com>
52 lines
2.4 KiB
ReStructuredText
52 lines
2.4 KiB
ReStructuredText
=========================================
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Hard Disk and File System Recommendations
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=========================================
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.. important:: Disable disk caching and asynchronous write.
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Ceph aims for data safety, which means that when the application receives notice that data was
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written to the disk, that data was actually written to the disk and not still in a transient state in
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a buffer or cache pending a lazy write to the hard disk.
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For data safety, you should mount your file system with caching disabled. Your file system should be
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mounted with ``sync`` and NOT ``async``. For example, your ``fstab`` file would reflect ``sync``. ::
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/dev/hda / xfs sync 0 0
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Use ``hdparm`` to disable write caching on the hard disk::
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$ hdparm -W 0 /dev/hda 0
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Ceph OSDs depend on the Extended Attributes (XATTRs) of the underlying file system for:
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- Internal object state
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- Snapshot metadata
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- RADOS Gateway Access Control Lists (ACLs).
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Ceph OSDs rely heavily upon the stability and performance of the underlying file system. The
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underlying file system must provide sufficient capacity for XATTRs. File system candidates for
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Ceph include B tree and B+ tree file systems such as:
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- ``btrfs``
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- ``XFS``
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.. warning:: XATTR limits.
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The RADOS Gateway's ACL and Ceph snapshots easily surpass the 4-kilobyte limit for XATTRs in ``ext4``,
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causing the ``ceph-osd`` process to crash. So ``ext4`` is a poor file system choice if
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you intend to deploy the RADOS Gateway or use snapshots. Version 0.45 or newer uses ``leveldb`` to
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bypass this limitation.
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.. tip:: Use ``xfs`` initially and ``btrfs`` when it is ready for production.
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The Ceph team believes that the best performance and stability will come from ``btrfs.``
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The ``btrfs`` file system has internal transactions that keep the local data set in a consistent state.
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This makes OSDs based on ``btrfs`` simple to deploy, while providing scalability not
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currently available from block-based file systems. The 64-kb XATTR limit for ``xfs``
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XATTRS is enough to accommodate RDB snapshot metadata and RADOS Gateway ACLs. So ``xfs`` is the second-choice
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file system of the Ceph team in the long run, but ``xfs`` is currently more stable than ``btrfs``.
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If you only plan to use RADOS and ``rbd`` without snapshots and without ``radosgw``, the ``ext4``
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file system should work just fine.
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