]>
Commit | Line | Data |
---|---|---|
1 | ===================== | |
2 | Erasure code profiles | |
3 | ===================== | |
4 | ||
5 | Erasure code is defined by a **profile** and is used when creating an | |
6 | erasure coded pool and the associated crush ruleset. | |
7 | ||
8 | The **default** erasure code profile (which is created when the Ceph | |
9 | cluster is initialized) provides the same level of redundancy as two | |
10 | copies but requires 25% less disk space. It is described as a profile | |
11 | with **k=2** and **m=1**, meaning the information is spread over three | |
12 | OSD (k+m == 3) and one of them can be lost. | |
13 | ||
14 | To improve redundancy without increasing raw storage requirements, a | |
15 | new profile can be created. For instance, a profile with **k=10** and | |
16 | **m=4** can sustain the loss of four (**m=4**) OSDs by distributing an | |
17 | object on fourteen (k+m=14) OSDs. The object is first divided in | |
18 | **10** chunks (if the object is 10MB, each chunk is 1MB) and **4** | |
19 | coding chunks are computed, for recovery (each coding chunk has the | |
20 | same size as the data chunk, i.e. 1MB). The raw space overhead is only | |
21 | 40% and the object will not be lost even if four OSDs break at the | |
22 | same time. | |
23 | ||
24 | .. _list of available plugins: | |
25 | ||
26 | .. toctree:: | |
27 | :maxdepth: 1 | |
28 | ||
29 | erasure-code-jerasure | |
30 | erasure-code-isa | |
31 | erasure-code-lrc | |
32 | erasure-code-shec | |
33 | ||
34 | osd erasure-code-profile set | |
35 | ============================ | |
36 | ||
37 | To create a new erasure code profile:: | |
38 | ||
39 | ceph osd erasure-code-profile set {name} \ | |
40 | [{directory=directory}] \ | |
41 | [{plugin=plugin}] \ | |
42 | [{stripe_unit=stripe_unit}] \ | |
43 | [{key=value} ...] \ | |
44 | [--force] | |
45 | ||
46 | Where: | |
47 | ||
48 | ``{directory=directory}`` | |
49 | ||
50 | :Description: Set the **directory** name from which the erasure code | |
51 | plugin is loaded. | |
52 | ||
53 | :Type: String | |
54 | :Required: No. | |
55 | :Default: /usr/lib/ceph/erasure-code | |
56 | ||
57 | ``{plugin=plugin}`` | |
58 | ||
59 | :Description: Use the erasure code **plugin** to compute coding chunks | |
60 | and recover missing chunks. See the `list of available | |
61 | plugins`_ for more information. | |
62 | ||
63 | :Type: String | |
64 | :Required: No. | |
65 | :Default: jerasure | |
66 | ||
67 | ``{stripe_unit=stripe_unit}`` | |
68 | ||
69 | :Description: The amount of data in a data chunk, per stripe. For | |
70 | example, a profile with 2 data chunks and stripe_unit=4K | |
71 | would put the range 0-4K in chunk 0, 4K-8K in chunk 1, | |
72 | then 8K-12K in chunk 0 again. This should be a multiple | |
73 | of 4K for best performance. The default value is taken | |
74 | from the monitor config option | |
75 | ``osd_pool_erasure_code_stripe_unit`` when a pool is | |
76 | created. The stripe_width of a pool using this profile | |
77 | will be the number of data chunks multiplied by this | |
78 | stripe_unit. | |
79 | ||
80 | :Type: String | |
81 | :Required: No. | |
82 | ||
83 | ``{key=value}`` | |
84 | ||
85 | :Description: The semantic of the remaining key/value pairs is defined | |
86 | by the erasure code plugin. | |
87 | ||
88 | :Type: String | |
89 | :Required: No. | |
90 | ||
91 | ``--force`` | |
92 | ||
93 | :Description: Override an existing profile by the same name, and allow | |
94 | setting a non-4K-aligned stripe_unit. | |
95 | ||
96 | :Type: String | |
97 | :Required: No. | |
98 | ||
99 | osd erasure-code-profile rm | |
100 | ============================ | |
101 | ||
102 | To remove an erasure code profile:: | |
103 | ||
104 | ceph osd erasure-code-profile rm {name} | |
105 | ||
106 | If the profile is referenced by a pool, the deletion will fail. | |
107 | ||
108 | osd erasure-code-profile get | |
109 | ============================ | |
110 | ||
111 | To display an erasure code profile:: | |
112 | ||
113 | ceph osd erasure-code-profile get {name} | |
114 | ||
115 | osd erasure-code-profile ls | |
116 | =========================== | |
117 | ||
118 | To list the names of all erasure code profiles:: | |
119 | ||
120 | ceph osd erasure-code-profile ls | |
121 |