Yes, when creating an EC profile, it automatically creates a CRUSH rule specific for that EC profile. You are also correct that 2+1 doesn't really have any resiliency built in. 2+2 would allow 1 node to go down while still having your data accessible. It will use 2x data to raw as opposed to the 1.5x of 2+1, but it gives you resiliency. The example in your command of 3+2 is not possible with your setup. May I ask why you want EC on such a small OSD count? I'm guessing to not use as much storage on your SSDs, but I would just suggest going with replica with such a small cluster. If you have a larger node/OSD count, then you can start seeing if EC is right for your use case, but if this is production data... I wouldn't risk it.
When setting the crush rule, it wants the name of it, ssdrule, not 2.
On Thu, Nov 1, 2018 at 1:34 PM Steven Vacaroaia <stef97@xxxxxxxxx> wrote:
_______________________________________________Hi,I am trying to create an EC pool on my SSD based OSDsand will appreciate if someone clarify / provide advice about the following- best K + M combination for 4 hosts one OSD per hostMy understanding is that K+M< OSD but using K=2, M=1 does not provide any redundancy( as soon as 1 OSD is down, you cannot write to the pool)Am I right ?- assigning crush_rule as per documentation does not seem to workIf I provide all the crush rule details when I create the EC profile, the PGs are being placed on SSD OSDs AND a crush rule is automatically createIs that the right/new way of doing it ?EXAMPLEceph osd erasure-code-profile set erasureISA crush-failure-domain=osd k=3 m=2 crush-root=ssds plugin=isa technique=cauchy crush-device-class=ssd[root@osd01 ~]# ceph osd crush rule lsreplicated_ruleerasure-codessdrule[root@osd01 ~]# ceph osd crush rule dump ssdrule{"rule_id": 2,"rule_name": "ssdrule","ruleset": 2,"type": 1,"min_size": 1,"max_size": 10,"steps": [{"op": "take","item": -4,"item_name": "ssds"},{"op": "chooseleaf_firstn","num": 0,"type": "host"},{"op": "emit"}]}[root@osd01 ~]# ceph osd pool set test crush_rule 2Error ENOENT: crush rule 2 does not exist
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