5 Erasure code is defined by a **profile** and is used when creating an
6 erasure coded pool and the associated crush ruleset.
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.
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
24 .. _list of available plugins:
34 osd erasure-code-profile set
35 ============================
37 To create a new erasure code profile::
39 ceph osd erasure-code-profile set {name} \
40 [{directory=directory}] \
42 [{stripe_unit=stripe_unit}] \
48 ``{directory=directory}``
50 :Description: Set the **directory** name from which the erasure code
55 :Default: /usr/lib/ceph/erasure-code
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.
67 ``{stripe_unit=stripe_unit}``
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
85 :Description: The semantic of the remaining key/value pairs is defined
86 by the erasure code plugin.
93 :Description: Override an existing profile by the same name, and allow
94 setting a non-4K-aligned stripe_unit.
99 osd erasure-code-profile rm
100 ============================
102 To remove an erasure code profile::
104 ceph osd erasure-code-profile rm {name}
106 If the profile is referenced by a pool, the deletion will fail.
108 osd erasure-code-profile get
109 ============================
111 To display an erasure code profile::
113 ceph osd erasure-code-profile get {name}
115 osd erasure-code-profile ls
116 ===========================
118 To list the names of all erasure code profiles::
120 ceph osd erasure-code-profile ls