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