Disclaimer: Even I will admit that I know this is going to sound like a
silly/crazy/insane question, but I have a reason for wanting to do this and
asking the question. It’s also worth noting that no active, production
workload will be used on this “cluster”, so I’m worried more about data
integrity than performance of availability.
Can anyone think of any catastrophic reason why I cannot use an existing
cluster’s CephFS filesystem as a single OSD for a small cluster? I’ve tested
it and it seems to work with the following caveats:
- 50% performance degradation (due to double write penalty since journal and
OSD data both are on the same backing cluster)
- Max object name and namespace length limits, which can be overcome with the
following OSD parameters:
- osd max object name len = 256
- osd max object namespace len = 64
- Due to above name/namespace length limits, cluster should be limited to RBD
(which is exactly what I want to do)
Some details of my cluster are below if anyone cares and I’m getting a
consistent, solid roughly 50% of the underlying cluster’s performance
benchmarks using “rados bench”:
# ceph --cluster cephfs status
cluster:
id: 0f8904ce-754b-48d4-aa58-7ee6fe9e2cca
health: HEALTH_OK
services:
mon: 1 daemons, quorum storage
mgr: storage(active)
osd: 1 osds: 1 up, 1 in
rbd-mirror: 1 daemon active
data:
pools: 1 pools, 32 pgs
objects: 10 objects, 133 B
usage: 12 MiB used, 87 GiB / 87 GiB avail
pgs: 32 active+clean
io:
client: 85 B/s wr, 0 op/s rd, 0 op/s wr
# ceph --cluster cephfs versions
{
"mon": {
"ceph version 13.2.4 (b10be4d44915a4d78a8e06aa31919e74927b142e) mimic
(stable)": 1
},
"mgr": {
"ceph version 13.2.4 (b10be4d44915a4d78a8e06aa31919e74927b142e) mimic
(stable)": 1
},
"osd": {
"ceph version 13.2.4 (b10be4d44915a4d78a8e06aa31919e74927b142e) mimic
(stable)": 1
},
"mds": {},
"rbd-mirror": {
"ceph version 13.2.4 (b10be4d44915a4d78a8e06aa31919e74927b142e) mimic
(stable)": 1
},
"overall": {
"ceph version 13.2.4 (b10be4d44915a4d78a8e06aa31919e74927b142e) mimic
(stable)": 4
}
}
# ceph --cluster cephfs osd df
ID CLASS WEIGHT REWEIGHT SIZE USE AVAIL %USE VAR PGS
0 hdd 0.08510 1.00000 87 GiB 16 MiB 87 GiB 0.02 1.00 32
TOTAL 87 GiB 16 MiB 87 GiB 0.02
MIN/MAX VAR: 1.00/1.00 STDDEV: 0
# ceph --cluster cephfs df
GLOBAL:
SIZE AVAIL RAW USED %RAW USED
87 GiB 87 GiB 16 MiB 0.02
POOLS:
NAME ID USED %USED MAX AVAIL OBJECTS
rbd 1 133 B 0 83 GiB 10
# df -h /var/lib/ceph/osd/cephfs-0/
Filesystem Size Used Avail Use% Mounted on
10.0.0.1:/ceph-remote 87G 12M 87G 1% /var/lib/ceph
Thanks,
--
Kenneth Van Alstyne
Systems Architect
Knight Point Systems, LLC
Service-Disabled Veteran-Owned Business
1775 Wiehle Avenue Suite 101 | Reston, VA 20190
c: 228-547-8045 f: 571-266-3106
www.knightpoint.com<http://www.knightpoint.com>
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GSA MOBIS Schedule: GS-10F-0404Y
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