Dear Mr Baergen,
thanks a lot for your very concise explanation,
however I would like to learn more why default Bluestore alloc.size causes such a big storage overhead,
and where in the Ceph docs it is explained how and what to watch for to avoid hitting this phenomenon again and again.
I have a feeling this is what I get on my experimental Ceph setup with simplest JErasure 2+1 data pool.
Could it be caused by journaled RBD writes to EC data-pool ?
Josh Baergen wrote:
Hey Arkadiy,
If the OSDs are on HDDs and were created with the default
bluestore_min_alloc_size_hdd, which is still 64KiB in Octopus, then in
effect data will be allocated from the pool in 640KiB chunks (64KiB *
(k+m)). 5.36M objects taking up 501GiB is an average object size of 98KiB
which results in a ratio of 6.53:1 allocated:stored, which is pretty close
to the 7:1 observed.
If my assumption about your configuration is correct, then the only way to
fix this is to adjust bluestore_min_alloc_size_hdd and recreate all your
OSDs, which will take a while...
Josh
On Tue, Jun 29, 2021 at 3:07 PM Arkadiy Kulev <eth@xxxxxxxxxxxx> wrote:
The pool *default.rgw.buckets.data* has *501 GiB* stored, but USED shows
*3.5
TiB *(7 times higher!)*:*
root@ceph-01:~# ceph df
--- RAW STORAGE ---
CLASS SIZE AVAIL USED RAW USED %RAW USED
hdd 196 TiB 193 TiB 3.5 TiB 3.6 TiB 1.85
TOTAL 196 TiB 193 TiB 3.5 TiB 3.6 TiB 1.85
--- POOLS ---
POOL ID PGS STORED OBJECTS USED %USED MAX
AVAIL
device_health_metrics 1 1 19 KiB 12 56 KiB 0
61 TiB
.rgw.root 2 32 2.6 KiB 6 1.1 MiB 0
61 TiB
default.rgw.log 3 32 168 KiB 210 13 MiB 0
61 TiB
default.rgw.control 4 32 0 B 8 0 B 0
61 TiB
default.rgw.meta 5 8 4.8 KiB 11 1.9 MiB 0
61 TiB
default.rgw.buckets.index 6 8 1.6 GiB 211 4.7 GiB 0
61 TiB
default.rgw.buckets.data 10 128 501 GiB 5.36M 3.5 TiB 1.90
110 TiB
The *default.rgw.buckets.data* pool is using erasure coding:
root@ceph-01:~# ceph osd erasure-code-profile get EC_RGW_HOST
crush-device-class=hdd
crush-failure-domain=host
crush-root=default
jerasure-per-chunk-alignment=false
k=6
m=4
plugin=jerasure
technique=reed_sol_van
w=8
If anyone could help explain why it's using up 7 times more space, it would
help a lot. Versioning is disabled. ceph version 15.2.13 (octopus stable).
Sincerely,
Ark.
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