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How to create an ec pool


alienn
37 Posts
January 11, 2019, 2:41 pm

Hi,

as written in the other section I created a new petasan cluster (24 OSDs, 3 journal drives). I wanted to use an ec pool, but I'm failing in creating one.

What did I do:

  • create a crush rule "ec-by-host-hdd" from template
  • create a crush rule "ec-by-host-ssd" from template
  • create an ec profile "ec-84-profile" (K8, M4; plugin: jerasure; technique: reed_sol_van)
  • add an pool (existing pool: 3 replicas, 512 placement groups):
    • name: ceph-ec-84
    • Pool type: EC
    • EC Profile: ec-84-profile
    • Number of PGs: 512
    • Min Size: 9
    • Compression: disabled
    • Rule Name: ec-by-host-hdd

The profile get created but never comes of the state "inactive". When investigating a little I found out that all new pgs are stale and never get distributed to any osds.

Can anyone tell me what I did wrong? I already redid the whole cluster twice, but always ran into the same problem.

The "replicated" pool is created normally and can be used normally.

 

Cheers,

alienn

#1

admin
2,930 Posts
January 11, 2019, 5:16 pm

The steps are correct, but you do not have enough nodes.

You chose a high ec profile : "ec-84-profile" (K8, M4) which makes 12 chunks per object.  The rule "by-host-hdd" will place each chunk on a host, so this setup requires 12 hosts.

To use ec pools, we recommend a min of 5 nodes to use 32 profile or much better 6 nodes  and use the 42 profile.

For 3 nodes you can use the 21 profile, but is not recommended.

#2

alienn
37 Posts
January 22, 2019, 4:30 pm

Thanks for this clarification. I thought that the chunks would be spread out over the osds and not over the hosts.

All in all it makes sense, but I had a severe misunderstanding here. 🙂

#3