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4da18aaf57
* add a field named "fmt_desc", which is the description formatted using reStructuredText. it is preserved as it is if it's different from the desc or long_desc of an option. we can consolidate it with long_desc in future, and use pretty printer which has minimal support for reStructuredText for printing the formatted descriptions for a better user experience of command line. but at this moment, fmt_desc has only one consumer: the "ceph_confval" sphinx extension which extracts and translate the options yaml file to reStructuredText, which is in turn rendered by sphinx. * remove unused options from the doc - journal_queue_max_ops - journal_queue_max_bytes Signed-off-by: Kefu Chai <kchai@redhat.com>
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1.8 KiB
ReStructuredText
40 lines
1.8 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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Filestore OSDs use a journal for two reasons: speed and consistency. Note
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that since Luminous, the BlueStore OSD back end has been preferred and default.
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This information is provided for pre-existing OSDs and for rare situations where
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Filestore is preferred for new deployments.
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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 file system 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 file system catches up to the
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journal.
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- **Consistency:** Ceph OSD Daemons require a file system 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 file system.
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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 file system, 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 recognize the following journal settings:
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.. confval:: journal_dio
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.. confval:: journal_aio
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.. confval:: journal_block_align
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.. confval:: journal_max_write_bytes
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.. confval:: journal_max_write_entries
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.. confval:: journal_align_min_size
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.. confval:: journal_zero_on_create
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