From: Anthony D'Atri Date: Tue, 29 Sep 2020 06:42:10 +0000 (-0700) Subject: doc/rados: erasure-code-lrc corrections X-Git-Tag: v16.1.0~940^2 X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=refs%2Fpull%2F37448%2Fhead;p=ceph.git doc/rados: erasure-code-lrc corrections doc/rados: erasure-code-lrc corrections - Clarified / corrected jerasure recovery characterization cf. https://library.eecs.utk.edu/storage/125phpw0xFqAut-cs-07-603.pdf - Capitalization - Word choice: OSDs are discrete / cardinal, so "fewer" instead of "less" - Reworked a few phrases to be less stilted Signed-off-by: Anthony D'Atri --- diff --git a/doc/rados/operations/erasure-code-lrc.rst b/doc/rados/operations/erasure-code-lrc.rst index a144b92eacf..b481b3d44c1 100644 --- a/doc/rados/operations/erasure-code-lrc.rst +++ b/doc/rados/operations/erasure-code-lrc.rst @@ -4,12 +4,12 @@ Locally repairable erasure code plugin With the *jerasure* plugin, when an erasure coded object is stored on multiple OSDs, recovering from the loss of one OSD requires reading -from all the others. For instance if *jerasure* is configured with -*k=8* and *m=4*, losing one OSD requires reading from the eight -others to repair. +from *k* others. For instance if *jerasure* is configured with +*k=8* and *m=4*, recovering from the loss of one OSD requires reading +from eight others. -The *lrc* erasure code plugin creates local parity chunks to be able -to recover using less OSDs. For instance if *lrc* is configured with +The *lrc* erasure code plugin creates local parity chunks to enable +recovery using fewer surviving OSDs. For instance if *lrc* is configured with *k=8*, *m=4* and *l=4*, it will create an additional parity chunk for every four OSDs. When a single OSD is lost, it can be recovered with only four OSDs instead of eight. @@ -34,7 +34,7 @@ observed.:: Reduce recovery bandwidth between racks --------------------------------------- -In Firefly the reduced bandwidth will only be observed if the primary +In Firefly the bandwidth reduction will only be observed if the primary OSD is in the same rack as the lost chunk.:: $ ceph osd erasure-code-profile set LRCprofile \ @@ -106,7 +106,7 @@ Where: ``crush-locality={bucket-type}`` -:Description: The type of the crush bucket in which each set of chunks +:Description: The type of the CRUSH bucket in which each set of chunks defined by **l** will be stored. For instance, if it is set to **rack**, each group of **l** chunks will be placed in a different rack. It is used to create a @@ -158,8 +158,8 @@ Low level plugin configuration ============================== The sum of **k** and **m** must be a multiple of the **l** parameter. -The low level configuration parameters do not impose such a -restriction and it may be more convenient to use it for specific +The low level configuration parameters however do not enforce this +restriction and it may be advantageous to use them for specific purposes. It is for instance possible to define two groups, one with 4 chunks and another with 3 chunks. It is also possible to recursively define locality sets, for instance datacenters and racks into