Notice

This document is for a development version of Ceph.

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} \
     [crush-root={root}] \
     [crush-failure-domain={bucket-type}] \
     [crush-device-class={device-class}] \
     [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. Choosing the right packet size is difficult. The jerasure documentation contains extensive information on this topic.

Type

Integer

Required

No.

Default

2048

crush-root={root}

Description

The name of the crush bucket used for the first step of the CRUSH rule. For instance step take default.

Type

String

Required

No.

Default

default

crush-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 CRUSH rule step such as step chooseleaf host.

Type

String

Required

No.

Default

host

crush-device-class={device-class}

Description

Restrict placement to devices of a specific class (e.g., ssd or hdd), using the crush device class names in the CRUSH map.

Type

String

Required

No.

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.