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. Chosing 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 intance 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.,
ssdorhdd), using the crush device class names in the CRUSH map.- Type:
String
- Required:
No.
- Default:
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.
