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              [ruleset-root={root}] \
  24              [ruleset-failure-domain={bucket-type}] \
  25              [directory={directory}] \
  26              [--force]
  27
  28 Where:
  29
  30 ``k={data chunks}``
  31
  32 :Description: Each object is split in **data-chunks** parts,
  33               each stored on a different OSD.
  34
  35 :Type: Integer
  36 :Required: Yes.
  37 :Example: 4
  38
  39 ``m={coding-chunks}``
  40
  41 :Description: Compute **coding chunks** for each object and store them
  42               on different OSDs. The number of coding chunks is also
  43               the number of OSDs that can be down without losing data.
  44
  45 :Type: Integer
  46 :Required: Yes.
  47 :Example: 2
  48
  49 ``technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion}``
  50
  51 :Description: The more flexible technique is *reed_sol_van* : it is
  52               enough to set *k* and *m*. The *cauchy_good* technique
  53               can be faster but you need to chose the *packetsize*
  54               carefully. All of *reed_sol_r6_op*, *liberation*,
  55               *blaum_roth*, *liber8tion* are *RAID6* equivalents in
  56               the sense that they can only be configured with *m=2*.
  57
  58 :Type: String
  59 :Required: No.
  60 :Default: reed_sol_van
  61
  62 ``packetsize={bytes}``
  63
  64 :Description: The encoding will be done on packets of *bytes* size at
  65               a time. Chosing the right packet size is difficult. The
  66               *jerasure* documentation contains extensive information
  67               on this topic.
  68
  69 :Type: Integer
  70 :Required: No.
  71 :Default: 2048
  72
  73 ``ruleset-root={root}``
  74
  75 :Description: The name of the crush bucket used for the first step of
  76               the ruleset. For intance **step take default**.
  77
  78 :Type: String
  79 :Required: No.
  80 :Default: default
  81
  82 ``ruleset-failure-domain={bucket-type}``
  83
  84 :Description: Ensure that no two chunks are in a bucket with the same
  85               failure domain. For instance, if the failure domain is
  86               **host** no two chunks will be stored on the same
  87               host. It is used to create a ruleset step such as **step
  88               chooseleaf host**.
  89
  90 :Type: String
  91 :Required: No.
  92 :Default: host
  93
  94 ``directory={directory}``
  95
  96 :Description: Set the **directory** name from which the erasure code
  97               plugin is loaded.
  98
  99 :Type: String
 100 :Required: No.
 101 :Default: /usr/lib/ceph/erasure-code
 102
 103 ``--force``
 104
 105 :Description: Override an existing profile by the same name.
 106
 107 :Type: String
 108 :Required: No.
 109