Hi Daniel,
the first thing to mention is, while min_size 2/size 3 is good, having
only three nodes leaves the cluster without any options to recover in
case of a node failure. So it 's recommended to use at least four nodes.
You have to be aware that the hybrid rule only gives you performance
advantages for read requests (from primary the OSD). Writing is only
completed when all replicas have acked the write, so your clients will
be waiting for the HDDs to ack.
The 5 TB are not wasted if you have other pools utilizing HDDs.
Regards,
Eugen
Zitat von Daniel Vogelbacher <daniel@xxxxxxxxxxxxxx>:
Hi,
I want to setup a 3-node Ceph cluster with fault domain configured to "host".
Each node should be equipped with:
6x SAS3 HDD 12TB
1x SAS3 SSD 7TB (should be extended to 2x7 later)
The ceph configuration should be size=3, min_size=2. All nodes are
connected with 2x10Gbit (LACP).
I want to use different CRUSH rules for different pools. CephFS and
low priority/IO VMs stored on RBD should use only HDD drives with
default replication CRUSH rule.
For high priority VMs, I want to create another RBD data pool which
uses a modified CRUSH replication rule:
|# Hybrid storage policy rule hybrid { ruleset 2 type replicated
step take ssd step chooseleaf firstn 1 type host step emit step take
hdd step chooseleaf firstn -1 type host step emit } |
|For pools using this hybrid rule, PGs are stored on one SSD
(primary) and two HDD (secondary) devices. But these have different
sizes in my hardware setup. What happens with the remaining disk
space (12-7=5) 5GB on the secondary devices? Is it just unusable, or
will ceph use it for other pools with default replication? In any
case, I don't bother about these 5GB, just want to know how it
works. For the above setup, can you recommend any important
configuration settings and should I modify the OSD weighting?
Thanks. |-- Best regards / Mit freundlichen Grüßen
Daniel Vogelbacher
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