Hi all,
We have (only) 2 separate "rooms" (crush bucket) and would like to build a cluster being able to handle the complete loss of one room.
First idea would be to use replication:
-> As we read the mail thread "2x replication: A BIG warning", we would chose a replication size of 3.
-> We need to change the default ruleset {bucket-type} to room. ( as described here http://docs.ceph.com/docs/master/rados/operations/crush-map/#crushmaprules )
We created for that a new crush rule:
rule replicated_ruleset_new {
ruleset 3
type replicated
min_size 1
max_size 10
step take default
step choose firstn 2 type room
step chooseleaf firstn 2 type host
step emit
}
Second idea would be to use Erasure Coding, as it fits our performance requirements and would use less raw space.
Creating an EC profile like:
?ceph osd erasure-code-profile set eck2m2room k=2 m=2 ruleset-failure-domain=room?
and a pool using that EC profile, with ?ceph osd pool create ecpool 128 128 erasure eck2m2room? of course leads to having ?128 creating+incomplete? PGs, as we only have 2 rooms.
Is there somehow a way to store the ?parity chuncks? (m) on both rooms, so that the loss of a room would be possible ?
If I understood correctly, an Erasure Coding of for example k=2, m=2, would use the same space as a replication with a size of 2, but be more reliable, as we could afford the loss of more OSDs at the same time.
Would it be possible to instruct the crush rule to store the first k and m chuncks in room 1, and the second k and m chuncks in room 2 ?
Many thanks for your feedbacks !
Thanks !
Fran?ois
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