+++ /dev/null
-Erasure Coded pool
-==================
-
-Purpose
--------
-
-Erasure-coded pools require less storage space compared to replicated
-pools. The erasure-coding support has higher computational requirements and
-only supports a subset of the operations allowed on an object (for instance,
-partial write is not supported).
-
-Use cases
----------
-
-Cold storage
-~~~~~~~~~~~~
-
-An erasure-coded pool is created to store a large number of 1GB
-objects (imaging, genomics, etc.) and 10% of them are read per
-month. New objects are added every day and the objects are not
-modified after being written. On average there is one write for 10,000
-reads.
-
-A replicated pool is created and set as a cache tier for the
-erasure coded pool. An agent demotes objects (i.e. moves them from the
-replicated pool to the erasure-coded pool) if they have not been
-accessed in a week.
-
-The erasure-coded pool crush ruleset targets hardware designed for
-cold storage with high latency and slow access time. The replicated
-pool crush ruleset targets faster hardware to provide better response
-times.
-
-Cheap multidatacenter storage
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Ten datacenters are connected with dedicated network links. Each
-datacenter contains the same amount of storage with no power-supply
-backup and no air-cooling system.
-
-An erasure-coded pool is created with a crush map ruleset that will
-ensure no data loss if at most three datacenters fail
-simultaneously. The overhead is 50% with erasure code configured to
-split data in six (k=6) and create three coding chunks (m=3). With
-replication the overhead would be 400% (four replicas).
-
-Interface
----------
-
-Set up an erasure-coded pool::
-
- $ ceph osd pool create ecpool 12 12 erasure
-
-Set up an erasure-coded pool and the associated crush ruleset::
-
- $ ceph osd crush rule create-erasure ecruleset
- $ ceph osd pool create ecpool 12 12 erasure \
- default ecruleset
-
-Set the ruleset failure domain to osd (instead of the host which is the default)::
-
- $ ceph osd erasure-code-profile set myprofile \
- crush-failure-domain=osd
- $ ceph osd erasure-code-profile get myprofile
- k=2
- m=1
- plugin=jerasure
- technique=reed_sol_van
- crush-failure-domain=osd
- $ ceph osd pool create ecpool 12 12 erasure myprofile
-
-Control the parameters of the erasure code plugin::
-
- $ ceph osd erasure-code-profile set myprofile \
- k=3 m=1
- $ ceph osd erasure-code-profile get myprofile
- k=3
- m=1
- plugin=jerasure
- technique=reed_sol_van
- $ ceph osd pool create ecpool 12 12 erasure \
- myprofile
-
-Choose an alternate erasure code plugin::
-
- $ ceph osd erasure-code-profile set myprofile \
- plugin=example technique=xor
- $ ceph osd erasure-code-profile get myprofile
- k=2
- m=1
- plugin=example
- technique=xor
- $ ceph osd pool create ecpool 12 12 erasure \
- myprofile
-
-Display the default erasure code profile::
-
- $ ceph osd erasure-code-profile ls
- default
- $ ceph osd erasure-code-profile get default
- k=2
- m=1
- plugin=jerasure
- technique=reed_sol_van
-
-Create a profile to set the data to be distributed on six OSDs (k+m=6) and sustain the loss of three OSDs (m=3) without losing data::
-
- $ ceph osd erasure-code-profile set myprofile k=3 m=3
- $ ceph osd erasure-code-profile get myprofile
- k=3
- m=3
- plugin=jerasure
- technique=reed_sol_van
- $ ceph osd erasure-code-profile ls
- default
- myprofile
-
-Remove a profile that is no longer in use (otherwise it will fail with EBUSY)::
-
- $ ceph osd erasure-code-profile ls
- default
- myprofile
- $ ceph osd erasure-code-profile rm myprofile
- $ ceph osd erasure-code-profile ls
- default
-
-Set the ruleset to take ssd (instead of default)::
-
- $ ceph osd erasure-code-profile set myprofile \
- crush-root=ssd
- $ ceph osd erasure-code-profile get myprofile
- k=2
- m=1
- plugin=jerasure
- technique=reed_sol_van
- crush-root=ssd
-
Code Review / stor4nfv.git / blobdiff