Hi Vincent, There is no buffering until the object reaches 8MB. When the object is written, it has a given size. RADOS just splits the object in K chunks, padding occurs if the object size is not a multiple of K.
See also: http://docs.ceph.com/docs/master/dev/osd_internals/erasure_coding/developer_notes/ Cheers, Maxime From: ceph-users <ceph-users-boun...@lists.ceph.com> on behalf of Vincent Godin <vince.ml...@gmail.com> Date: Tuesday 21 March 2017 17:16 To: ceph-users <ceph-users@lists.ceph.com> Subject: [ceph-users] Need erasure coding, pg and block size explanation When we use a replicated pool of size 3 for example, each data, a block of 4MB is written on one PG which is distributed on 3 hosts (by default). The osd holding the primary will copy the block to OSDs holding the secondary and third PG. With erasure code, let's take a raid5 schema like k=2 and m=1. Does Ceph buffer the data till it reach a amount of 8 MB which it can then divide into two blocks of 4MB and a parity control of 4MB ? Does it just divide the data in two chunks whatever the size ? Will it use then PG1 on OSD.A to store the first block, PG1 on OSD.X to store the second block of data and PG1 on OSD.z to store the parity ? Thanks for your explanation because i didn't found any clear explanation on how data chunk and parity
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