Hello, What is your current setup, 1 server pet data center with 12 osd each? What is your current crush rule and LRC crush rule? On Fri, Apr 28, 2023, 12:29 Michel Jouvin <michel.jouvin@ijclab.in2p3.fr> wrote:
Hi,
I think I found a possible cause of my PG down but still understand why. As explained in a previous mail, I setup a 15-chunk/OSD EC pool (k=9, m=6) but I have only 12 OSD servers in the cluster. To workaround the problem I defined the failure domain as 'osd' with the reasoning that as I was using the LRC plugin, I had the warranty that I could loose a site without impact, thus the possibility to loose 1 OSD server. Am I wrong?
Best regards,
Michel
Le 24/04/2023 à 13:24, Michel Jouvin a écrit :
Hi,
I'm still interesting by getting feedback from those using the LRC plugin about the right way to configure it... Last week I upgraded from Pacific to Quincy (17.2.6) with cephadm which is doing the upgrade host by host, checking if an OSD is ok to stop before actually upgrading it. I had the surprise to see 1 or 2 PGs down at some points in the upgrade (happened not for all OSDs but for every site/datacenter). Looking at the details with "ceph health detail", I saw that for these PGs there was 3 OSDs down but I was expecting the pool to be resilient to 6 OSDs down (5 for R/W access) so I'm wondering if there is something wrong in our pool configuration (k=9, m=6, l=5).
Cheers,
Michel
Le 06/04/2023 à 08:51, Michel Jouvin a écrit :
Hi,
Is somebody using LRC plugin ?
I came to the conclusion that LRC k=9, m=3, l=4 is not the same as jerasure k=9, m=6 in terms of protection against failures and that I should use k=9, m=6, l=5 to get a level of resilience >= jerasure k=9, m=6. The example in the documentation (k=4, m=2, l=3) suggests that this LRC configuration gives something better than jerasure k=4, m=2 as it is resilient to 3 drive failures (but not 4 if I understood properly). So how many drives can fail in the k=9, m=6, l=5 configuration first without loosing RW access and second without loosing data?
Another thing that I don't quite understand is that a pool created with this configuration (and failure domain=osd, locality=datacenter) has a min_size=3 (max_size=18 as expected). It seems wrong to me, I'd expected something ~10 (depending on answer to the previous question)...
Thanks in advance if somebody could provide some sort of authoritative answer on these 2 questions. Best regards,
Michel
Le 04/04/2023 à 15:53, Michel Jouvin a écrit :
Answering to myself, I found the reason for 2147483647: it's documented as a failure to find enough OSD (missing OSDs). And it is normal as I selected different hosts for the 15 OSDs but I have only 12 hosts!
I'm still interested by an "expert" to confirm that LRC k=9, m=3, l=4 configuration is equivalent, in terms of redundancy, to a jerasure configuration with k=9, m=6.
Michel
Le 04/04/2023 à 15:26, Michel Jouvin a écrit :
Hi,
As discussed in another thread (Crushmap rule for multi-datacenter erasure coding), I'm trying to create an EC pool spanning 3 datacenters (datacenters are present in the crushmap), with the objective to be resilient to 1 DC down, at least keeping the readonly access to the pool and if possible the read-write access, and have a storage efficiency better than 3 replica (let say a storage overhead <= 2).
In the discussion, somebody mentioned LRC plugin as a possible jerasure alternative to implement this without tweaking the crushmap rule to implement the 2-step OSD allocation. I looked at the documentation (https://docs.ceph.com/en/latest/rados/operations/erasure-code-lrc/) but I have some questions if someone has experience/expertise with this LRC plugin.
I tried to create a rule for using 5 OSDs per datacenter (15 in total), with 3 (9 in total) being data chunks and others being coding chunks. For this, based of my understanding of examples, I used k=9, m=3, l=4. Is it right? Is this configuration equivalent, in terms of redundancy, to a jerasure configuration with k=9, m=6?
The resulting rule, which looks correct to me, is:
--------
{ "rule_id": 6, "rule_name": "test_lrc_2", "ruleset": 6, "type": 3, "min_size": 3, "max_size": 15, "steps": [ { "op": "set_chooseleaf_tries", "num": 5 }, { "op": "set_choose_tries", "num": 100 }, { "op": "take", "item": -4, "item_name": "default~hdd" }, { "op": "choose_indep", "num": 3, "type": "datacenter" }, { "op": "chooseleaf_indep", "num": 5, "type": "host" }, { "op": "emit" } ] }
------------
Unfortunately, it doesn't work as expected: a pool created with this rule ends up with its pages active+undersize, which is unexpected for me. Looking at 'ceph health detail` output, I see for each page something like:
pg 52.14 is stuck undersized for 27m, current state active+undersized, last acting
[90,113,2147483647,103,64,147,164,177,2147483647,133,58,28,8,32,2147483647]
For each PG, there is 3 '2147483647' entries and I guess it is the reason of the problem. What are these entries about? Clearly it is not OSD entries... Looks like a negative number, -1, which in terms of crushmap ID is the crushmap root (named "default" in our configuration). Any trivial mistake I would have made?
Thanks in advance for any help or for sharing any successful configuration?
Best regards,
Michel _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
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