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doc/rados/operations: Clarify overwrites in erasure-code.rst
Signed-off-by: Anthony D'Atri <[email protected]>
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doc/rados/operations/erasure-code.rst

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@@ -177,10 +177,10 @@ Erasure Coding with Overwrites
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------------------------------
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By default, erasure-coded pools work only with operations that
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perform full object writes and appends (for example, RGW).
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perform full RADOS object writes, for example, RGW.
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Since Luminous, partial writes for an erasure-coded pool may be
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enabled with a per-pool setting. This lets RBD and CephFS store their
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enabled with a per-pool setting. This lets RBD, CephFS, and librados store
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data in an erasure-coded pool:
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.. prompt:: bash $
@@ -189,13 +189,16 @@ data in an erasure-coded pool:
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This can be enabled only on a pool residing on BlueStore OSDs, since
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BlueStore's checksumming is used during deep scrubs to detect bitrot
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or other corruption. Using Filestore with EC overwrites is not only
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and other corruption. Using Filestore with EC overwrites is not only
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unsafe, but it also results in lower performance compared to BlueStore.
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Moreover, Filestore is deprecated and any Filestore OSDs in your cluster
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should be migrated to BlueStore.
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There is no downside to enabling EC overwrites, so it is best practice to
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routinely do so.
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Erasure-coded pools do not support omap, so to use them with RBD and
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CephFS you must instruct them to store their data in an EC pool and
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CephFS you must instruct them and their clients to store their data in an EC pool and
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their metadata in a replicated pool. For RBD, this means using the
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erasure-coded pool as the ``--data-pool`` during image creation:
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@@ -213,7 +216,8 @@ Erasure Coding Optimizations
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Since Tentacle, an erasure-coded pool may have optimizations enabled
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with a per-pool setting. This improves performance for smaller I/Os and
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eliminates padding which can save capacity:
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eliminates padding, which can significantly reduce space amplification
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and wasted capacity:
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.. prompt:: bash $
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