Additional issue with the disk usage statistics I've just realized is
that BlueStore's statfs call reports total disk space as
block device total space + DB device total space
while available space is measured as
block device's free space + bluefs free space at block device -
bluestore_bluefs_free param
This results in higher used space value (as available space at DB
device isn't taken into account) and odd results when cluster is
(almost) empty.
IMO we shouldn't use DB device for total space calculation.
Sage, what do you think?
Thanks,
Igor
On 12/26/2017 6:25 AM, Zhi Zhang wrote:
Hi,
We recently started to test bluestore with huge amount of small files
(only dozens of bytes per file). We have 22 OSDs in a test cluster
using ceph-12.2.1 with 2 replicas and each OSD disk is 2TB size. After
we wrote about 150 million files through cephfs, we found each OSD
disk usage reported by "ceph osd df" was more than 40%, which meant
more than 800GB was used for each disk, but the actual total file size
was only about 5.2 GB, which was reported by "ceph df" and also
calculated by ourselves.
The test is ongoing. I wonder whether the cluster would report OSD
full after we wrote about 300 million files, however the actual total
file size would be far far less than the disk usage. I will update the
result when the test is done.
My question is, whether the disk usage statistics in bluestore is
inaccurate, or the padding, alignment stuff or something else in
bluestore wastes the disk space?
Thanks!
$ ceph osd df
ID CLASS WEIGHT REWEIGHT SIZE USE AVAIL %USE VAR PGS
0 hdd 1.49728 1.00000 1862G 853G 1009G 45.82 1.00 110
1 hdd 1.69193 1.00000 1862G 807G 1054G 43.37 0.94 105
2 hdd 1.81929 1.00000 1862G 811G 1051G 43.57 0.95 116
3 hdd 2.00700 1.00000 1862G 839G 1023G 45.04 0.98 122
4 hdd 2.06334 1.00000 1862G 886G 976G 47.58 1.03 130
5 hdd 1.99051 1.00000 1862G 856G 1006G 45.95 1.00 118
6 hdd 1.67519 1.00000 1862G 881G 981G 47.32 1.03 114
7 hdd 1.81929 1.00000 1862G 874G 988G 46.94 1.02 120
8 hdd 2.08881 1.00000 1862G 885G 976G 47.56 1.03 130
9 hdd 1.64265 1.00000 1862G 852G 1010G 45.78 0.99 106
10 hdd 1.81929 1.00000 1862G 873G 989G 46.88 1.02 109
11 hdd 2.20041 1.00000 1862G 915G 947G 49.13 1.07 131
12 hdd 1.45694 1.00000 1862G 874G 988G 46.94 1.02 110
13 hdd 2.03847 1.00000 1862G 821G 1041G 44.08 0.96 113
14 hdd 1.53812 1.00000 1862G 810G 1052G 43.50 0.95 112
15 hdd 1.52914 1.00000 1862G 874G 988G 46.94 1.02 111
16 hdd 1.99176 1.00000 1862G 810G 1052G 43.51 0.95 114
17 hdd 1.81929 1.00000 1862G 841G 1021G 45.16 0.98 119
18 hdd 1.70901 1.00000 1862G 831G 1031G 44.61 0.97 113
19 hdd 1.67519 1.00000 1862G 875G 987G 47.02 1.02 115
20 hdd 2.03847 1.00000 1862G 864G 998G 46.39 1.01 115
21 hdd 2.18794 1.00000 1862G 920G 942G 49.39 1.07 127
TOTAL 40984G 18861G 22122G 46.02
$ ceph df
GLOBAL:
SIZE AVAIL RAW USED %RAW USED
40984G 22122G 18861G 46.02
POOLS:
NAME ID USED %USED MAX AVAIL OBJECTS
cephfs_metadata 5 160M 0 6964G 77342
cephfs_data 6 5193M 0.04 6964G 151292669
Regards,
Zhi Zhang (David)
Contact: zhang.david2011@xxxxxxxxx
zhangz.david@xxxxxxxxxxx
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