rbd create --size 1G --data-pool ec_pool replicated_pool/image_name
For CephFS, an erasure-coded pool can be set as the default data pool during
-file system creation or via `file layouts <../../../cephfs/file-layouts>`_.
+file system creation or via :ref:`file-layouts`.
+ Erasure Coding Optimizations
+ ----------------------------
+
+ Since Tentacle, an erasure-coded pool may have optimizations enabled
+ with a per-pool setting. This improves performance for smaller I/Os and
+ eliminates padding which can save capacity:
+
+ .. prompt:: bash $
+
+ ceph osd pool set ec_pool allow_ec_optimizations true
+
+ The optimizations will make an erasure code pool more suitable for use
+ with RBD or CephFS. For RGW workloads that have large objects that are read and
+ written sequentially there will be little benefit from these optimizations; but
+ RGW workloads with lots of very small objects or small random access reads will
+ see performance and capacity benefits.
+
+ This flag may be enabled for existing pools, and can be configured
+ to default for new pools using the central configuration option
+ :confval:`osd_pool_default_flag_ec_optimizations`. Once the flag has been
+ enabled for a pool it cannot be disabled because it changes how new data is
+ stored.
+
+ The flag cannot be set unless all the Monitors and OSDs have been
+ upgraded to Tentacle or later. Optimizations can be enabled and used without
+ upgrading gateways and clients.
+
+ Optimizations are currently only supported with the Jerasure and ISA-L plugins
+ when using the ``reed_sol_van`` technique (these are the old and current
+ defaults and are the most widely used plugins and technique). Attempting to
+ set the flag for a pool using an unsupported combination of plugin and
+ technique is blocked with an error message.
+
+ The default stripe unit is 4K which works well for standard EC pools.
+ For the majority of I/O workloads it is recommended to increase the stripe
+ unit to at least 16K when using optimizations. Performance testing
+ shows that 16K is the best choice for general purpose I/O workloads. Increasing
+ this value will significantly improve small read performance but will slightly
+ reduce the performance of small sequential writes. For I/O workloads that are
+ predominately reads, larger values up to 256KB will further improve read
+ performance but will further reduce the performance of small sequential writes.
+ Values larger than 256KB are unlikely to have any performance benefit. The
+ stripe unit is a pool create-time option that can be set in the erasure code
+ profile or by setting the central configuration option
+ :confval:`osd_pool_erasure_code_stripe_unit`. The stripe unit cannot be changed
+ after the pool has been created, so if enabling optimizations for an existing
+ pool you will not get the full benefit of the optimizations.
+
+ Without optimizations enabled, the choice of ``k+m`` in the erasure code profile
+ affects performance. The higher the values of ``k`` and ``m`` the lower the
+ performance will be. With optimizations enabled there is only a very slight
+ reduction in performance as ``k`` increases so this makes using a higher value
+ of ``k`` more viable. Increasing ``m`` still impacts write performance,
+ especially for small writes, so for block and file workloads a value of ``m``
+ no larger than 3 is recommended.
+
Erasure-coded pool overhead
---------------------------
projects / ceph.git / commitdiff