ceph/doc/rados/operations/erasure-code-jerasure.rst

   1 ============================
   2 Jerasure erasure code plugin
   3 ============================
   4
   5 The *jerasure* plugin is the most generic and flexible plugin, it is
   6 also the default for Ceph erasure coded pools.
   7
   8 The *jerasure* plugin encapsulates the `Jerasure
   9 <https://github.com/ceph/jerasure>`_ library. It is
  10 recommended to read the ``jerasure`` documentation to
  11 understand the parameters. Note that the ``jerasure.org``
  12 web site as of 2023 may no longer be connected to the original
  13 project or legitimate.
  14
  15 Create a jerasure profile
  16 =========================
  17
  18 To create a new *jerasure* erasure code profile:
  19
  20 .. prompt:: bash $
  21
  22    ceph osd erasure-code-profile set {name} \
  23      plugin=jerasure \
  24      k={data-chunks} \
  25      m={coding-chunks} \
  26      technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion} \
  27      [crush-root={root}] \
  28      [crush-failure-domain={bucket-type}] \
  29      [crush-device-class={device-class}] \
  30      [directory={directory}] \
  31      [--force]
  32
  33 Where:
  34
  35 ``k={data chunks}``
  36
  37 :Description: Each object is split in **data-chunks** parts,
  38               each stored on a different OSD.
  39
  40 :Type: Integer
  41 :Required: Yes.
  42 :Example: 4
  43
  44 ``m={coding-chunks}``
  45
  46 :Description: Compute **coding chunks** for each object and store them
  47               on different OSDs. The number of coding chunks is also
  48               the number of OSDs that can be down without losing data.
  49
  50 :Type: Integer
  51 :Required: Yes.
  52 :Example: 2
  53
  54 ``technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion}``
  55
  56 :Description: The more flexible technique is *reed_sol_van* : it is
  57               enough to set *k* and *m*. The *cauchy_good* technique
  58               can be faster but you need to chose the *packetsize*
  59               carefully. All of *reed_sol_r6_op*, *liberation*,
  60               *blaum_roth*, *liber8tion* are *RAID6* equivalents in
  61               the sense that they can only be configured with *m=2*.
  62
  63 :Type: String
  64 :Required: No.
  65 :Default: reed_sol_van
  66
  67 ``packetsize={bytes}``
  68
  69 :Description: The encoding will be done on packets of *bytes* size at
  70               a time. Choosing the right packet size is difficult. The
  71               *jerasure* documentation contains extensive information
  72               on this topic.
  73
  74 :Type: Integer
  75 :Required: No.
  76 :Default: 2048
  77
  78 ``crush-root={root}``
  79
  80 :Description: The name of the crush bucket used for the first step of
  81               the CRUSH rule. For instance **step take default**.
  82
  83 :Type: String
  84 :Required: No.
  85 :Default: default
  86
  87 ``crush-failure-domain={bucket-type}``
  88
  89 :Description: Ensure that no two chunks are in a bucket with the same
  90               failure domain. For instance, if the failure domain is
  91               **host** no two chunks will be stored on the same
  92               host. It is used to create a CRUSH rule step such as **step
  93               chooseleaf host**.
  94
  95 :Type: String
  96 :Required: No.
  97 :Default: host
  98
  99 ``crush-device-class={device-class}``
 100
 101 :Description: Restrict placement to devices of a specific class (e.g.,
 102               ``ssd`` or ``hdd``), using the crush device class names
 103               in the CRUSH map.
 104
 105 :Type: String
 106 :Required: No.
 107
 108 ``directory={directory}``
 109
 110 :Description: Set the **directory** name from which the erasure code
 111               plugin is loaded.
 112
 113 :Type: String
 114 :Required: No.
 115 :Default: /usr/lib/ceph/erasure-code
 116
 117 ``--force``
 118
 119 :Description: Override an existing profile by the same name.
 120
 121 :Type: String
 122 :Required: No.
 123