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https://github.com/ceph/ceph
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117 lines
3.1 KiB
ReStructuredText
117 lines
3.1 KiB
ReStructuredText
==========================
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Journal Config Reference
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==========================
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.. index:: journal; journal configuration
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Ceph OSDs use a journal for two reasons: speed and consistency.
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- **Speed:** The journal enables the Ceph OSD Daemon to commit small writes
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quickly. Ceph writes small, random i/o to the journal sequentially, which
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tends to speed up bursty workloads by allowing the backing filesystem more
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time to coalesce writes. The Ceph OSD Daemon's journal, however, can lead
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to spiky performance with short spurts of high-speed writes followed by
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periods without any write progress as the filesystem catches up to the
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journal.
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- **Consistency:** Ceph OSD Daemons require a filesystem interface that
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guarantees atomic compound operations. Ceph OSD Daemons write a description
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of the operation to the journal and apply the operation to the filesystem.
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This enables atomic updates to an object (for example, placement group
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metadata). Every few seconds--between ``filestore max sync interval`` and
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``filestore min sync interval``--the Ceph OSD Daemon stops writes and
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synchronizes the journal with the filesystem, allowing Ceph OSD Daemons to
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trim operations from the journal and reuse the space. On failure, Ceph
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OSD Daemons replay the journal starting after the last synchronization
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operation.
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Ceph OSD Daemons support the following journal settings:
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``journal dio``
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:Description: Enables direct i/o to the journal. Requires ``journal block
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align`` set to ``true``.
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:Type: Boolean
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:Required: Yes when using ``aio``.
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:Default: ``true``
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``journal aio``
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.. versionchanged:: 0.61 Cuttlefish
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:Description: Enables using ``libaio`` for asynchronous writes to the journal.
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Requires ``journal dio`` set to ``true``.
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:Type: Boolean
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:Required: No.
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:Default: Version 0.61 and later, ``true``. Version 0.60 and earlier, ``false``.
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``journal block align``
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:Description: Block aligns write operations. Required for ``dio`` and ``aio``.
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:Type: Boolean
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:Required: Yes when using ``dio`` and ``aio``.
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:Default: ``true``
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``journal max write bytes``
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:Description: The maximum number of bytes the journal will write at
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any one time.
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:Type: Integer
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:Required: No
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:Default: ``10 << 20``
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``journal max write entries``
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:Description: The maximum number of entries the journal will write at
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any one time.
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:Type: Integer
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:Required: No
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:Default: ``100``
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``journal queue max ops``
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:Description: The maximum number of operations allowed in the queue at
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any one time.
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:Type: Integer
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:Required: No
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:Default: ``500``
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``journal queue max bytes``
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:Description: The maximum number of bytes allowed in the queue at
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any one time.
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:Type: Integer
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:Required: No
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:Default: ``10 << 20``
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``journal align min size``
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:Description: Align data payloads greater than the specified minimum.
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:Type: Integer
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:Required: No
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:Default: ``64 << 10``
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``journal zero on create``
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:Description: Causes the file store to overwrite the entire journal with
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``0``'s during ``mkfs``.
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:Type: Boolean
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:Required: No
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:Default: ``false``
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