[ceph-users] Ceph cache pool full

Christian Balzer chibi at gol.com
Fri Oct 6 09:31:16 PDT 2017


On Fri, 6 Oct 2017 09:14:40 -0700 Shawfeng Dong wrote:

> I found the command: rados -p cephfs_cache cache-flush-evict-all
> 
That's not what you want/need.
Though it will fix your current "full" issue.

> The documentation (
> http://docs.ceph.com/docs/luminous/rados/operations/cache-tiering/) has
> been improved a lot since I last checked it a few weeks ago!
>
The need to set max_bytes and max_objects has been documented for ages
(since Hammer).

more below...

> -Shaw
> 
> On Fri, Oct 6, 2017 at 9:10 AM, Shawfeng Dong <shaw at ucsc.edu> wrote:
> 
> > Thanks, Luis.
> >
> > I've just set max_bytes and max_objects:
How?
Editing the conf file won't help until a restart.

> > target_max_objects: 1000000 (1M)
> > target_max_bytes: 1099511627776 (1TB)
>
I'd lower that or the cache_target_full_ratio by another 10%.

Christian
> >
> > but nothing appears to be happening. Is there a way to force flushing?
> >
> > Thanks,
> > Shaw
> >
> > On Fri, Oct 6, 2017 at 8:55 AM, Luis Periquito <periquito at gmail.com>
> > wrote:
> >  
> >> Not looking at anything else, you didn't set the max_bytes or
> >> max_objects for it to start flushing...
> >>
> >> On Fri, Oct 6, 2017 at 4:49 PM, Shawfeng Dong <shaw at ucsc.edu> wrote:  
> >> > Dear all,
> >> >
> >> > Thanks a lot for the very insightful comments/suggestions!
> >> >
> >> > There are 3 OSD servers in our pilot Ceph cluster, each with 2x 1TB SSDs
> >> > (boot disks), 12x 8TB SATA HDDs and 2x 1.2TB NVMe SSDs. We use the  
> >> bluestore  
> >> > backend, with the first NVMe as the WAL and DB devices for OSDs on the  
> >> HDDs.  
> >> > And we try to create a cache tier out of the second NVMes.
> >> >
> >> > Here are the outputs of the commands suggested by David:
> >> >
> >> > 1) # ceph df
> >> > GLOBAL:
> >> >     SIZE     AVAIL     RAW USED     %RAW USED
> >> >     265T      262T        2847G          1.05
> >> > POOLS:
> >> >     NAME                ID     USED      %USED      MAX AVAIL  
> >>  OBJECTS  
> >> >     cephfs_data         1          0          0          248T  
> >>  0  
> >> >     cephfs_metadata     2      8515k          0          248T  
> >> 24  
> >> >     cephfs_cache        3      1381G     100.00             0  
> >> 355385  
> >> >
> >> > 2) # ceph osd df
> >> >  0   hdd 7.27829  1.00000 7452G 2076M  7450G  0.03  0.03 174
> >> >  1   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 169
> >> >  2   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 173
> >> >  3   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 159
> >> >  4   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 173
> >> >  5   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 162
> >> >  6   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 149
> >> >  7   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 179
> >> >  8   hdd 7.27829  1.00000 7452G 2076M  7450G  0.03  0.03 163
> >> >  9   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 194
> >> > 10   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 185
> >> > 11   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 168
> >> > 36  nvme 1.09149  1.00000 1117G  855G   262G 76.53 73.01  79
> >> > 12   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 180
> >> > 13   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 168
> >> > 14   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 178
> >> > 15   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 170
> >> > 16   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 149
> >> > 17   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 203
> >> > 18   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 173
> >> > 19   hdd 7.27829  1.00000 7452G 2076M  7450G  0.03  0.03 158
> >> > 20   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 154
> >> > 21   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 160
> >> > 22   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 167
> >> > 23   hdd 7.27829  1.00000 7452G 2076M  7450G  0.03  0.03 188
> >> > 37  nvme 1.09149  1.00000 1117G 1061G 57214M 95.00 90.63  98
> >> > 24   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 187
> >> > 25   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 200
> >> > 26   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 147
> >> > 27   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 171
> >> > 28   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 162
> >> > 29   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 152
> >> > 30   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 174
> >> > 31   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 176
> >> > 32   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 182
> >> > 33   hdd 7.27829  1.00000 7452G 2072M  7450G  0.03  0.03 155
> >> > 34   hdd 7.27829  1.00000 7452G 2076M  7450G  0.03  0.03 166
> >> > 35   hdd 7.27829  1.00000 7452G 2076M  7450G  0.03  0.03 176
> >> > 38  nvme 1.09149  1.00000 1117G  857G   260G 76.71 73.18  79
> >> >                     TOTAL  265T 2847G   262T  1.05
> >> > MIN/MAX VAR: 0.03/90.63  STDDEV: 22.81
> >> >
> >> > 3) # ceph osd tree
> >> > -1       265.29291 root default
> >> > -3        88.43097     host pulpo-osd01
> >> >  0   hdd   7.27829         osd.0            up  1.00000 1.00000
> >> >  1   hdd   7.27829         osd.1            up  1.00000 1.00000
> >> >  2   hdd   7.27829         osd.2            up  1.00000 1.00000
> >> >  3   hdd   7.27829         osd.3            up  1.00000 1.00000
> >> >  4   hdd   7.27829         osd.4            up  1.00000 1.00000
> >> >  5   hdd   7.27829         osd.5            up  1.00000 1.00000
> >> >  6   hdd   7.27829         osd.6            up  1.00000 1.00000
> >> >  7   hdd   7.27829         osd.7            up  1.00000 1.00000
> >> >  8   hdd   7.27829         osd.8            up  1.00000 1.00000
> >> >  9   hdd   7.27829         osd.9            up  1.00000 1.00000
> >> > 10   hdd   7.27829         osd.10           up  1.00000 1.00000
> >> > 11   hdd   7.27829         osd.11           up  1.00000 1.00000
> >> > 36  nvme   1.09149         osd.36           up  1.00000 1.00000
> >> > -5        88.43097     host pulpo-osd02
> >> > 12   hdd   7.27829         osd.12           up  1.00000 1.00000
> >> > 13   hdd   7.27829         osd.13           up  1.00000 1.00000
> >> > 14   hdd   7.27829         osd.14           up  1.00000 1.00000
> >> > 15   hdd   7.27829         osd.15           up  1.00000 1.00000
> >> > 16   hdd   7.27829         osd.16           up  1.00000 1.00000
> >> > 17   hdd   7.27829         osd.17           up  1.00000 1.00000
> >> > 18   hdd   7.27829         osd.18           up  1.00000 1.00000
> >> > 19   hdd   7.27829         osd.19           up  1.00000 1.00000
> >> > 20   hdd   7.27829         osd.20           up  1.00000 1.00000
> >> > 21   hdd   7.27829         osd.21           up  1.00000 1.00000
> >> > 22   hdd   7.27829         osd.22           up  1.00000 1.00000
> >> > 23   hdd   7.27829         osd.23           up  1.00000 1.00000
> >> > 37  nvme   1.09149         osd.37           up  1.00000 1.00000
> >> > 36  nvme   1.09149         osd.36           up  1.00000 1.00000
> >> > -5        88.43097     host pulpo-osd02
> >> > 12   hdd   7.27829         osd.12           up  1.00000 1.00000
> >> > 13   hdd   7.27829         osd.13           up  1.00000 1.00000
> >> > 14   hdd   7.27829         osd.14           up  1.00000 1.00000
> >> > 15   hdd   7.27829         osd.15           up  1.00000 1.00000
> >> > 16   hdd   7.27829         osd.16           up  1.00000 1.00000
> >> > 17   hdd   7.27829         osd.17           up  1.00000 1.00000
> >> > 18   hdd   7.27829         osd.18           up  1.00000 1.00000
> >> > 19   hdd   7.27829         osd.19           up  1.00000 1.00000
> >> > 20   hdd   7.27829         osd.20           up  1.00000 1.00000
> >> > 21   hdd   7.27829         osd.21           up  1.00000 1.00000
> >> > 22   hdd   7.27829         osd.22           up  1.00000 1.00000
> >> > 23   hdd   7.27829         osd.23           up  1.00000 1.00000
> >> > 37  nvme   1.09149         osd.37           up  1.00000 1.00000
> >> > -7        88.43097     host pulpo-osd03
> >> > 24   hdd   7.27829         osd.24           up  1.00000 1.00000
> >> > 25   hdd   7.27829         osd.25           up  1.00000 1.00000
> >> > 26   hdd   7.27829         osd.26           up  1.00000 1.00000
> >> > 27   hdd   7.27829         osd.27           up  1.00000 1.00000
> >> > 28   hdd   7.27829         osd.28           up  1.00000 1.00000
> >> > 29   hdd   7.27829         osd.29           up  1.00000 1.00000
> >> > 30   hdd   7.27829         osd.30           up  1.00000 1.00000
> >> > 31   hdd   7.27829         osd.31           up  1.00000 1.00000
> >> > 32   hdd   7.27829         osd.32           up  1.00000 1.00000
> >> > 33   hdd   7.27829         osd.33           up  1.00000 1.00000
> >> > 34   hdd   7.27829         osd.34           up  1.00000 1.00000
> >> > 35   hdd   7.27829         osd.35           up  1.00000 1.00000
> >> > 38  nvme   1.09149         osd.38           up  1.00000 1.00000
> >> >
> >> > 4) # ceph osd pool get cephfs_cache all
> >> > min_size: 2
> >> > crash_replay_interval: 0
> >> > pg_num: 128
> >> > pgp_num: 128
> >> > crush_rule: pulpo_nvme
> >> > hashpspool: true
> >> > nodelete: false
> >> > nopgchange: false
> >> > nosizechange: false
> >> > write_fadvise_dontneed: false
> >> > noscrub: false
> >> > nodeep-scrub: false
> >> > hit_set_type: bloom
> >> > hit_set_period: 14400
> >> > hit_set_count: 12
> >> > hit_set_fpp: 0.05
> >> > use_gmt_hitset: 1
> >> > auid: 0
> >> > target_max_objects: 0
> >> > target_max_bytes: 0
> >> > cache_target_dirty_ratio: 0.4
> >> > cache_target_dirty_high_ratio: 0.6
> >> > cache_target_full_ratio: 0.8
> >> > cache_min_flush_age: 0
> >> > cache_min_evict_age: 0
> >> > min_read_recency_for_promote: 0
> >> > min_write_recency_for_promote: 0
> >> > fast_read: 0
> >> > hit_set_grade_decay_rate: 0
> >> > crash_replay_interval: 0
> >> >
> >> > Do you see anything wrong? We had written some small files to the CephFS
> >> > before we tried to write the big 1TB file. What is puzzling to me is  
> >> that no  
> >> > data has been written back to the data pool.
> >> >
> >> > Best,
> >> > Shaw
> >> >
> >> > On Fri, Oct 6, 2017 at 6:46 AM, David Turner <drakonstein at gmail.com>  
> >> wrote:  
> >> >>
> >> >>
> >> >>
> >> >> On Fri, Oct 6, 2017, 1:05 AM Christian Balzer <chibi at gol.com> wrote:  
> >> >>>
> >> >>>
> >> >>> Hello,
> >> >>>
> >> >>> On Fri, 06 Oct 2017 03:30:41 +0000 David Turner wrote:
> >> >>>  
> >> >>> > You're missing most all of the important bits. What the osds in your
> >> >>> > cluster look like, your tree, and your cache pool settings.
> >> >>> >
> >> >>> > ceph df
> >> >>> > ceph osd df
> >> >>> > ceph osd tree
> >> >>> > ceph osd pool get cephfs_cache all
> >> >>> >  
> >> >>> Especially the last one.
> >> >>>
> >> >>> My money is on not having set target_max_objects and target_max_bytes  
> >> to  
> >> >>> sensible values along with the ratios.
> >> >>> In short, not having read the (albeit spotty) documentation.
> >> >>>  
> >> >>> > You have your writeback cache on 3 nvme drives. It looks like you  
> >> have  
> >> >>> > 1.6TB available between them for the cache. I don't know the  
> >> behavior  
> >> >>> > of a
> >> >>> > writeback cache tier on cephfs for large files, but I would guess  
> >> that  
> >> >>> > it
> >> >>> > can only hold full files and not flush partial files.  
> >> >>>
> >> >>> I VERY much doubt that, if so it would be a massive flaw.
> >> >>> One assumes that cache operations work on the RADOS object level, no
> >> >>> matter what.  
> >> >>
> >> >> I hope that it is on the rados level, but not a single object had been
> >> >> flushed to the backing pool. So I hazarded a guess. Seeing his  
> >> settings will  
> >> >> shed more light.  
> >> >>>
> >> >>>  
> >> >>> > That would mean your
> >> >>> > cache needs to have enough space for any file being written to the
> >> >>> > cluster.
> >> >>> > In this case a 1.3TB file with 3x replication would require 3.9TB  
> >> (more  
> >> >>> > than double what you have available) of available space in your
> >> >>> > writeback
> >> >>> > cache.
> >> >>> >
> >> >>> > There are very few use cases that benefit from a cache tier. The  
> >> docs  
> >> >>> > for
> >> >>> > Luminous warn as much.  
> >> >>> You keep repeating that like a broken record.
> >> >>>
> >> >>> And while certainly not false I for one wouldn't be able to use  
> >> (justify  
> >> >>> using) Ceph w/o cache tiers in our main use case.
> >> >>>
> >> >>>
> >> >>> In this case I assume they were following and old cheat sheet or such,
> >> >>> suggesting the previously required cache tier with EC pools.  
> >> >>
> >> >>
> >> >> http://docs.ceph.com/docs/luminous/rados/operations/cache-tiering/
> >> >>
> >> >> I know I keep repeating it, especially recently as there have been a  
> >> lot  
> >> >> of people asking about it. The Luminous docs added a large section  
> >> about how  
> >> >> it is probably not what you want. Like me, it is not saying that there  
> >> are  
> >> >> no use cases for it. There was no information provided about the use  
> >> case  
> >> >> and I made some suggestions/guesses. I'm also guessing that they are
> >> >> following a guide where a writeback cache was necessary for CephFS to  
> >> use EC  
> >> >> prior to Luminous. I also usually add that people should test it out  
> >> and  
> >> >> find what works best for them. I will always defer to your practical  
> >> use of  
> >> >> cache tiers as well, especially when using rbds.
> >> >>
> >> >> I manage a cluster that I intend to continue running a writeback cache  
> >> in  
> >> >> front of CephFS on the same drives as the EC pool. The use case  
> >> receives a  
> >> >> good enough benefit from the cache tier that it isn't even required to  
> >> use  
> >> >> flash media to see it. It is used for video editing and the files are
> >> >> usually modified and read within the first 24 hours and then left in  
> >> cold  
> >> >> storage until deleted. I have the cache timed to keep everything in it  
> >> for  
> >> >> 24 hours and then evict it by using a minimum time to flush and evict  
> >> at 24  
> >> >> hours and a target max bytes of 0. All files are in there for that  
> >> time and  
> >> >> then it never has to decide what to keep as it doesn't keep anything  
> >> longer  
> >> >> than that. Luckily read performance from cold storage is not a  
> >> requirement  
> >> >> of this cluster as any read operation has to first read it from EC  
> >> storage,  
> >> >> write it to replica storage, and then read it from replica storage...  
> >> Yuck.  
> >> >>>
> >> >>>
> >> >>> Christian
> >> >>>  
> >> >>> >What is your goal by implementing this cache? If the
> >> >>> > answer is to utilize extra space on the nvmes, then just remove it  
> >> and  
> >> >>> > say
> >> >>> > thank you. The better use of nvmes in that case are as a part of the
> >> >>> > bluestore stack and give your osds larger DB partitions. Keeping  
> >> your  
> >> >>> > metadata pool on nvmes is still a good idea.
> >> >>> >
> >> >>> > On Thu, Oct 5, 2017, 7:45 PM Shawfeng Dong <shaw at ucsc.edu> wrote:
> >> >>> >  
> >> >>> > > Dear all,
> >> >>> > >
> >> >>> > > We just set up a Ceph cluster, running the latest stable release  
> >> Ceph  
> >> >>> > > v12.2.0 (Luminous):
> >> >>> > > # ceph --version
> >> >>> > > ceph version 12.2.0 (32ce2a3ae5239ee33d6150705cdb24d43bab910c)
> >> >>> > > luminous
> >> >>> > > (rc)
> >> >>> > >
> >> >>> > > The goal is to serve Ceph filesystem, for which we created 3  
> >> pools:  
> >> >>> > > # ceph osd lspools
> >> >>> > > 1 cephfs_data,2 cephfs_metadata,3 cephfs_cache,
> >> >>> > > where
> >> >>> > > * cephfs_data is the data pool (36 OSDs on HDDs), which is
> >> >>> > > erased-coded;
> >> >>> > > * cephfs_metadata is the metadata pool
> >> >>> > > * cephfs_cache is the cache tier (3 OSDs on NVMes) for  
> >> cephfs_data.  
> >> >>> > > The
> >> >>> > > cache-mode is writeback.
> >> >>> > >
> >> >>> > > Everything had worked fine, until today when we tried to copy a  
> >> 1.3TB  
> >> >>> > > file
> >> >>> > > to the CephFS.  We got the "No space left on device" error!
> >> >>> > >
> >> >>> > > 'ceph -s' says some OSDs are full:
> >> >>> > > # ceph -s
> >> >>> > >   cluster:
> >> >>> > >     id:     e18516bf-39cb-4670-9f13-88ccb7d19769
> >> >>> > >     health: HEALTH_ERR
> >> >>> > >             full flag(s) set
> >> >>> > >             1 full osd(s)
> >> >>> > >             1 pools have many more objects per pg than average
> >> >>> > >
> >> >>> > >   services:
> >> >>> > >     mon: 3 daemons, quorum pulpo-admin,pulpo-mon01,pulpo-mds01
> >> >>> > >     mgr: pulpo-mds01(active), standbys: pulpo-admin, pulpo-mon01
> >> >>> > >     mds: pulpos-1/1/1 up  {0=pulpo-mds01=up:active}
> >> >>> > >     osd: 39 osds: 39 up, 39 in
> >> >>> > >          flags full
> >> >>> > >
> >> >>> > >   data:
> >> >>> > >     pools:   3 pools, 2176 pgs
> >> >>> > >     objects: 347k objects, 1381 GB
> >> >>> > >     usage:   2847 GB used, 262 TB / 265 TB avail
> >> >>> > >     pgs:     2176 active+clean
> >> >>> > >
> >> >>> > >   io:
> >> >>> > >     client:   19301 kB/s rd, 2935 op/s rd, 0 op/s wr
> >> >>> > >
> >> >>> > > And indeed the cache pool is full:
> >> >>> > > # rados df
> >> >>> > > POOL_NAME       USED  OBJECTS CLONES COPIES MISSING_ON_PRIMARY
> >> >>> > > UNFOUND
> >> >>> > > DEGRADED RD_OPS   RD
> >> >>> > >     WR_OPS  WR
> >> >>> > > cephfs_cache    1381G  355385      0 710770                  0
> >> >>> > > 0
> >> >>> > >     0 10004954 15
> >> >>> > > 22G 1398063  1611G
> >> >>> > > cephfs_data         0       0      0      0                  0
> >> >>> > > 0
> >> >>> > >     0        0
> >> >>> > >   0       0      0
> >> >>> > > cephfs_metadata 8515k      24      0     72                  0
> >> >>> > > 0
> >> >>> > >     0        3  3
> >> >>> > > 072    3953 10541k
> >> >>> > >
> >> >>> > > total_objects    355409
> >> >>> > > total_used       2847G
> >> >>> > > total_avail      262T
> >> >>> > > total_space      265T
> >> >>> > >
> >> >>> > > However, the data pool is completely empty! So it seems that data  
> >> has  
> >> >>> > > only
> >> >>> > > been written to the cache pool, but not written back to the data
> >> >>> > > pool.
> >> >>> > >
> >> >>> > > I am really at a loss whether this is due to a setup error on my
> >> >>> > > part, or
> >> >>> > > a Luminous bug. Could anyone shed some light on this? Please let  
> >> me  
> >> >>> > > know if
> >> >>> > > you need any further info.
> >> >>> > >
> >> >>> > > Best,
> >> >>> > > Shaw
> >> >>> > > _______________________________________________
> >> >>> > > ceph-users mailing list
> >> >>> > > ceph-users at lists.ceph.com
> >> >>> > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> >> >>> > >  
> >> >>>
> >> >>>
> >> >>> --
> >> >>> Christian Balzer        Network/Systems Engineer
> >> >>> chibi at gol.com           Rakuten Communications
> >> >>> _______________________________________________
> >> >>> ceph-users mailing list
> >> >>> ceph-users at lists.ceph.com
> >> >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com  
> >> >>
> >> >>
> >> >> _______________________________________________
> >> >> ceph-users mailing list
> >> >> ceph-users at lists.ceph.com
> >> >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> >> >>  
> >> >
> >> >
> >> > _______________________________________________
> >> > ceph-users mailing list
> >> > ceph-users at lists.ceph.com
> >> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> >> >  
> >>  
> >
> >  


-- 
Christian Balzer        Network/Systems Engineer                
chibi at gol.com   	Rakuten Communications


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