Jerasure erasure code plugin

The jerasure plugin is the most generic and flexible plugin, it is also the default for Ceph erasure coded pools.

The jerasure plugin encapsulates the Jerasure library. It is recommended to read the jerasure documentation to get a better understanding of the parameters.

Create a jerasure profile

To create a new jerasure erasure code profile:

ceph osd erasure-code-profile set {name} \
     plugin=jerasure \
     k={data-chunks} \
     m={coding-chunks} \
     technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion} \
     [ruleset-root={root}] \
     [ruleset-failure-domain={bucket-type}] \
     [directory={directory}] \
     [--force]

Where:

k={data chunks}

Description:Each object is split in data-chunks parts, each stored on a different OSD. Type:Integer Required:Yes. Example:4

m={coding-chunks}

Description:Compute coding chunks for each object and store them on different OSDs. The number of coding chunks is also the number of OSDs that can be down without losing data. Type:Integer Required:Yes. Example:2

technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion}

Description:The more flexible technique is reed_sol_van : it is enough to set k and m. The cauchy_good technique can be faster but you need to chose the packetsize carefully. All of reed_sol_r6_op, liberation, blaum_roth, liber8tion are RAID6 equivalents in the sense that they can only be configured with m=2. Type:String Required:No. Default:reed_sol_van

packetsize={bytes}

Description:The encoding will be done on packets of bytes size at a time. Chosing the right packet size is difficult. The jerasure documentation contains extensive information on this topic. Type:Integer Required:No. Default:2048

ruleset-root={root}

Description:The name of the crush bucket used for the first step of the ruleset. For intance step take default. Type:String Required:No. Default:default

ruleset-failure-domain={bucket-type}

Description:Ensure that no two chunks are in a bucket with the same failure domain. For instance, if the failure domain is host no two chunks will be stored on the same host. It is used to create a ruleset step such as step chooseleaf host. Type:String Required:No. Default:host

directory={directory}

Description:Set the directory name from which the erasure code plugin is loaded. Type:String Required:No. Default:/usr/lib/ceph/erasure-code

--force

Description:Override an existing profile by the same name. Type:String Required:No.