Hi, No... our current setup is 3 datacenters with the same configuration, i.e. 1 mon/mgr + 4 OSD servers with 16 OSDs each. Thus the total of 12 OSDs servers. As with LRC plugin, k+m must be a multiple of l, I found that k=9/m=66/l=5 with crush-locality=datacenter was achieving my goal of being resilient to a datacenter failure. Because I had this, I considered that lowering the crush failure domain to osd was not a major issue in my case (as it would not be worst than a datacenter failure if all the shards are on the same server in a datacenter) and was working around the lack of hosts for k=9/m=6 (15 OSDs). May be it helps, if I give the erasure code profile used: crush-device-class=hdd crush-failure-domain=osd crush-locality=datacenter crush-root=default k=9 l=5 m=6 plugin=lrc The previously mentioned strange number for min_size for the pool created with this profile has vanished after Quincy upgrade as this parameter is no longer in the CRUH map rule! and the `ceph osd pool get` command reports the expected number (10): ---------
ceph osd pool get fink-z1.rgw.buckets.data min_size min_size: 10
Cheers, Michel Le 29/04/2023 à 20:36, Curt a écrit :
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 _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io