> -----Original Message----- > From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Piotr Dzionek > Sent: 30 November 2016 11:04 > To: Brad Hubbard <bhubbard@xxxxxxxxxx> > Cc: Ceph Users <ceph-users@xxxxxxxxxxxxxx> > Subject: Re: - cluster stuck and undersized if at least one osd is down > > Hi, > > Ok, but I still don't get what advantage would I get from blocked IOs. > If I set size=2 and min_size=2 and during rebuild another disk dies on the other node, I will loose data. I know that I should set size=3, > it is the much safer. But I don't see what is the advantage of blocked io ? > Maybe you mean faster rebuild ? or maybe if there is no IOs the likehood of another disk failure drops ? You need to think about exotic scenarios where an OSD may fail for other reasons than just a straight disk failure. Probably the most dangerous times are when OSD's start flapping for what other reasons. You can quickly get into a situation where an object is updated on a single remaining OSD. If this OSD now goes down and other copy comes back up, Ceph will mark the object unfound as it's not the latest version of the object. If whatever reason this OSD with the latest copy is no longer available, you now have dataloss. There are several mailing list posts and blogs where people have had several days outages and data loss caused by this situation. I experienced 2 OSD's dying a couple of weeks ago after deleting a large snapshot somehow got them in an inconsistent state after OSD's all over the cluster were flapping. If I was using min_size=1, I know I would have lost objects. I'm not convinced a size=2 min_size=1 is completely safe on OSD's over RAID either. Whilst you are protected from a disk failing scenario. Flapping or OSD bug is still just as likely to cause data loss. > > > W dniu 30.11.2016 o 04:39, Brad Hubbard pisze: > > > > On Tue, Nov 29, 2016 at 11:37 PM, Piotr Dzionek <piotr.dzionek@xxxxxxxx> wrote: > >> Hi, > >> > >> As far as I understand if I set pool size 2, there is a chance to > >> loose data when another osd dies while there is rebuild ongoing. > >> However, it has to occur on the different host, because my crushmap > >> forbids to store replicas on the same physical node. > > I am not talking about size, I am talking specifically about min_size, > > regardless of size. > > > >> I am not sure what would change if I set min_size 2, because the only > >> thing I would get is that there is no IOs to objects with less than 2 > >> replicas, while there is rebuild ongoing. And in that case > > Which is exactly what you should want if you are concerened about data > > integrity. If you allow IO via min_size to be served by a single OSD > > via > > min_size=1 and you tehn lose that OSD you will lose any changes to the > > pgs resulting in inconsistency and missing objects. You are removing > > the consistency guarantees that ceph provides. So if you use > > min_size=1 you need to be comfortable with the fact that there is a > > likelihood you *will* lose data at some stage. Usually this is not what people implementing ceph want. > > > >> my vms wouldn't be able to read data from ceph pool. But maybe I got > >> it wrong. > >> > >> > >> W dniu 29.11.2016 o 03:08, Brad Hubbard pisze: > >> > >>> On Mon, Nov 28, 2016 at 9:54 PM, Piotr Dzionek > >>> <piotr.dzionek@xxxxxxxx> > >>> wrote: > >>>> Hi, > >>>> I recently installed 3 nodes ceph cluster v.10.2.3. It has 3 mons, > >>>> and 12 osds. I removed default pool and created the following one: > >>>> > >>>> pool 7 'data' replicated size 2 min_size 1 crush_ruleset 0 > >>>> object_hash rjenkins pg_num 1024 pgp_num 1024 last_change 126 flags > >>>> hashpspool stripe_width 0 > >>> Do you understand the significance of min_size 1? > >>> > >>> Are you OK with the likelihood of data loss that this value introduces? > >>> > >>>> Cluster is healthy if all osds are up, however if I stop any of the > >>>> osds, it becomes stuck and undersized - it is not rebuilding. > >>>> > >>>> cluster ***** > >>>> health HEALTH_WARN > >>>> 166 pgs degraded > >>>> 108 pgs stuck unclean > >>>> 166 pgs undersized > >>>> recovery 67261/827220 objects degraded (8.131%) > >>>> 1/12 in osds are down > >>>> monmap e3: 3 mons at > >>>> {**osd01=***.144:6789/0,***osd02=***.145:6789/0,**osd03=*****.146:6789/0} > >>>> election epoch 14, quorum 0,1,2 **osd01,**osd02,**osd03 > >>>> osdmap e161: 12 osds: 11 up, 12 in; 166 remapped pgs > >>>> flags sortbitwise > >>>> pgmap v307710: 1024 pgs, 1 pools, 1230 GB data, 403 kobjects > >>>> 2452 GB used, 42231 GB / 44684 GB avail > >>>> 67261/827220 objects degraded (8.131%) > >>>> 858 active+clean > >>>> 166 active+undersized+degraded > >>>> > >>>> Replica size is 2 and and I use the following crushmap: > >>>> > >>>> # begin crush map > >>>> tunable choose_local_tries 0 > >>>> tunable choose_local_fallback_tries 0 tunable choose_total_tries 50 > >>>> tunable chooseleaf_descend_once 1 tunable chooseleaf_vary_r 1 > >>>> tunable straw_calc_version 1 > >>>> > >>>> # devices > >>>> device 0 osd.0 > >>>> device 1 osd.1 > >>>> device 2 osd.2 > >>>> device 3 osd.3 > >>>> device 4 osd.4 > >>>> device 5 osd.5 > >>>> device 6 osd.6 > >>>> device 7 osd.7 > >>>> device 8 osd.8 > >>>> device 9 osd.9 > >>>> device 10 osd.10 > >>>> device 11 osd.11 > >>>> > >>>> # types > >>>> type 0 osd > >>>> type 1 host > >>>> type 2 chassis > >>>> type 3 rack > >>>> type 4 row > >>>> type 5 pdu > >>>> type 6 pod > >>>> type 7 room > >>>> type 8 datacenter > >>>> type 9 region > >>>> type 10 root > >>>> > >>>> # buckets > >>>> host osd01 { > >>>> id -2 # do not change unnecessarily > >>>> # weight 14.546 > >>>> alg straw > >>>> hash 0 # rjenkins1 > >>>> item osd.0 weight 3.636 > >>>> item osd.1 weight 3.636 > >>>> item osd.2 weight 3.636 > >>>> item osd.3 weight 3.636 > >>>> } > >>>> host osd02 { > >>>> id -3 # do not change unnecessarily > >>>> # weight 14.546 > >>>> alg straw > >>>> hash 0 # rjenkins1 > >>>> item osd.4 weight 3.636 > >>>> item osd.5 weight 3.636 > >>>> item osd.6 weight 3.636 > >>>> item osd.7 weight 3.636 > >>>> } > >>>> host osd03 { > >>>> id -4 # do not change unnecessarily > >>>> # weight 14.546 > >>>> alg straw > >>>> hash 0 # rjenkins1 > >>>> item osd.8 weight 3.636 > >>>> item osd.9 weight 3.636 > >>>> item osd.10 weight 3.636 > >>>> item osd.11 weight 3.636 > >>>> } > >>>> root default { > >>>> id -1 # do not change unnecessarily > >>>> # weight 43.637 > >>>> alg straw > >>>> hash 0 # rjenkins1 > >>>> item osd01 weight 14.546 > >>>> item osd02 weight 14.546 > >>>> item osd03 weight 14.546 > >>>> } > >>>> > >>>> # rules > >>>> rule replicated_ruleset { > >>>> ruleset 0 > >>>> type replicated > >>>> min_size 1 > >>>> max_size 10 > >>>> step take default > >>>> step chooseleaf firstn 0 type host > >>>> step emit > >>>> } > >>>> > >>>> # end crush map > >>>> > >>>> I am not sure what is the reason for undersized state. All osd > >>>> disks are the same size and replica size is 2. Also data is only > >>>> replicated per hosts basis and I have 3 separate hosts. Maybe > >>>> number of pg is incorrect ? Is > >>>> 1024 too big ? or maybe there is some misconfiguration in crushmap ? > >>>> > >>>> > >>>> Kind regards, > >>>> Piotr Dzionek > >>>> > >>>> > >>>> _______________________________________________ > >>>> ceph-users mailing list > >>>> ceph-users@xxxxxxxxxxxxxx > >>>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > >>>> > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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