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| -rw-r--r-- | doc/rados/operations/erasure-code.rst | 19 |
1 files changed, 11 insertions, 8 deletions
diff --git a/doc/rados/operations/erasure-code.rst b/doc/rados/operations/erasure-code.rst index 288369526db..ca267594135 100644 --- a/doc/rados/operations/erasure-code.rst +++ b/doc/rados/operations/erasure-code.rst @@ -50,10 +50,10 @@ requires at least three hosts: Erasure code profiles --------------------- -The default erasure code profile sustains the loss of a two OSDs. It -is equivalent to a replicated pool of size three but requires 2TB -instead of 3TB to store 1TB of data. The default profile can be -displayed with: +The default erasure code profile can sustain the loss of two OSDs. This erasure +code profile is equivalent to a replicated pool of size three, but requires +2TB to store 1TB of data instead of 3TB to store 1TB of data. The default +profile can be displayed with this command: .. prompt:: bash $ @@ -67,13 +67,16 @@ displayed with: crush-failure-domain=host technique=reed_sol_van -Choosing the right profile is important because it cannot be modified -after the pool is created: a new pool with a different profile needs -to be created and all objects from the previous pool moved to the new. +Choosing the right profile is important because the profile cannot be modified +after the pool is created. If you find that you need an erasure-coded pool with +a profile different than the one you have created, you must create a new pool +with a different (and presumably more carefully-considered) profile. When the +new pool is created, all objects from the wrongly-configured pool must be moved +to the newly-created pool. There is no way to alter the profile of a pool after its creation. The most important parameters of the profile are *K*, *M* and *crush-failure-domain* because they define the storage overhead and -the data durability. For instance, if the desired architecture must +the data durability. For example, if the desired architecture must sustain the loss of two racks with a storage overhead of 67% overhead, the following profile can be defined: |