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52 lines
2.2 KiB
ReStructuredText
52 lines
2.2 KiB
ReStructuredText
=========================================
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Hard Disk and File System Recommendations
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=========================================
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Ceph aims for data safety, which means that when the application receives notice
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that data was written to the disk, that data was actually written to the disk.
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For old kernels (<2.6.33), disable the write cache if the journal is on a raw
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disk. Newer kernels should work fine.
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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
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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
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system. The underlying file system must provide sufficient capacity for XATTRs.
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File system candidates for 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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If you are using ``ext4``, enable XATTRs. ::
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filestore xattr use omap = true
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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
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for XATTRs in ``ext4``, causing the ``ceph-osd`` process to crash. Version 0.45
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or newer uses ``leveldb`` to bypass this limitation. ``ext4`` is a poor file
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system choice if you intend to deploy the RADOS Gateway or use snapshots on
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versions earlier than 0.45.
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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
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``btrfs.`` The ``btrfs`` file system has internal transactions that keep the
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local data set in a consistent state. This makes OSDs based on ``btrfs`` simple
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to deploy, while providing scalability not currently available from block-based
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file systems. The 64-kb XATTR limit for ``xfs`` XATTRS is enough to accommodate
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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
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stable than ``btrfs``. If you only plan to use RADOS and ``rbd`` without
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snapshots and without ``radosgw``, the ``ext4`` file system should work just fine.
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