Journal配置手册Journal Config Reference?
# 写Journal，可以让大量的随机写小块数据转变成写连续的Journal。 # 同时后台文件系统有更多时间合并小块数据，再写盘。 # 写Journal有可能带来性能上的毛刺，因为该场景是，短时间大量写请求的到来，紧接着没有任何写请求，只有文件系统在追Journal。 Ceph OSDs use a journal for two reasons: speed and consistency.
- Speed: The journal enables the Ceph OSD Daemon to commit small writes
quickly. Ceph writes small, random i/o to the journal sequentially, which
tends to speed up bursty workloads by allowing the backing filesystem more
time to coalesce writes. The Ceph OSD Daemon’s journal, however, can lead
to spiky performance with short spurts of high-speed writes followed by
periods without any write progress as the filesystem catches up to the
journal.
- Consistency: Ceph OSD Daemons require a filesystem interface that
guarantees atomic compound operations. Ceph OSD Daemons write a description
of the operation to the journal and apply the operation to the filesystem.
This enables atomic updates to an object (for example, placement group
metadata). Every few seconds–between filestore max sync interval and
filestore min sync interval–the Ceph OSD Daemon stops writes and
synchronizes the journal with the filesystem, allowing Ceph OSD Daemons to
trim（调整） operations from the journal and reuse the space. On failure, Ceph
OSD Daemons replay the journal starting after the last synchronization
operation.
Ceph OSD Daemons support the following journal settings:
journal dio
| Description: | Enables direct i/o to the journal. Requires journal block
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
Changed in version 0.61: Cuttlefish
| Description: | Enables using libaio for asynchronous writes to the journal.
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
| 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 每次写Journal 最大写10M
| Description: | The maximum number of bytes the journal will write at
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
| Description: | The maximum number of entries the journal will write at
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
| Description: | The maximum number of operations allowed in the queue at
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
| Description: | The maximum number of bytes allowed in the queue at
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
| 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
| Description: | Causes the file store to overwrite the entire journal with
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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