From: Anthony D'Atri Date: Sat, 6 May 2023 00:43:15 +0000 (-0400) Subject: doc/rados/configuration: correct space amp in bluestore-config-ref.rst X-Git-Tag: v19.0.0~1273^2 X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=79256c12139a75390d734b8e1bf5f3fdc6754a9d;p=ceph.git doc/rados/configuration: correct space amp in bluestore-config-ref.rst Signed-off-by: Anthony D'Atri --- diff --git a/doc/rados/configuration/bluestore-config-ref.rst b/doc/rados/configuration/bluestore-config-ref.rst index 37b3c43d7ca3..44dd6cdd8708 100644 --- a/doc/rados/configuration/bluestore-config-ref.rst +++ b/doc/rados/configuration/bluestore-config-ref.rst @@ -431,7 +431,7 @@ GateWay (RGW) deployments that host large numbers of small files For example, when an RGW client stores a 1KB S3 object, it is written to a single RADOS object. With the default :confval:`min_alloc_size` value, 4KB of underlying drive space is allocated. This means that roughly -(4KB - 1KB) == 3KB is allocated but never used, which corresponds to 300% +(4KB - 1KB) == 3KB of that RADOS object's allocated space is never used, which corresponds to 300% overhead or 25% efficiency. Similarly, a 5KB user object will be stored as one 4KB and one 1KB RADOS object, again stranding 4KB of device capacity, though in this case the overhead is a much smaller percentage. Think of this @@ -440,8 +440,8 @@ thus decreases rapidly as user object size increases. An easily missed additional subtlety is that this takes place for *each* replica. So when using the default three copies of -data (3R), a 1KB S3 object actually consumes roughly 9KB of storage device -capacity. If erasure coding (EC) is used instead of replication, the +data (3R), a 1KB S3 object actually consumes 12KB of storage device +capacity, with 11KB of overhead. If erasure coding (EC) is used instead of replication, the amplification may be even higher: for a ``k=4,m=2`` pool, our 1KB S3 object will allocate (6 * 4KB) = 24KB of device capacity.