Is there anybody who can explain the overcommitment calcuation? Thanks Mon, 28 Oct 2019 11:24:54 +0100 Lars Täuber <taeuber@xxxxxxx> ==> ceph-users <ceph-users@xxxxxxx> : > Is there a way to get rid of this warnings with activated autoscaler besides adding new osds? > > Yet I couldn't get a satisfactory answer to the question why this all happens. > > ceph osd pool autoscale-status : > POOL SIZE TARGET SIZE RATE RAW CAPACITY RATIO TARGET RATIO BIAS PG_NUM NEW PG_NUM AUTOSCALE > cephfs_data 122.2T 1.5 165.4T 1.1085 0.8500 1.0 1024 on > > versus > > ceph df : > RAW STORAGE: > CLASS SIZE AVAIL USED RAW USED %RAW USED > hdd 165 TiB 41 TiB 124 TiB 124 TiB 74.95 > > POOLS: > POOL ID STORED OBJECTS USED %USED MAX AVAIL > cephfs_data 1 75 TiB 49.31M 122 TiB 87.16 12 TiB > > > It seems that the overcommitment is wrongly calculated. Isn't the RATE already used to calculate the SIZE? > > It seems USED(df) = SIZE(autoscale-status) > Isn't the RATE already taken into account here? > > Could someone please explain the numbers to me? > > > Thanks! > Lars > > Fri, 25 Oct 2019 07:42:58 +0200 > Lars Täuber <taeuber@xxxxxxx> ==> Nathan Fish <lordcirth@xxxxxxxxx> : > > Hi Nathan, > > > > Thu, 24 Oct 2019 10:59:55 -0400 > > Nathan Fish <lordcirth@xxxxxxxxx> ==> Lars Täuber <taeuber@xxxxxxx> : > > > Ah, I see! The BIAS reflects the number of placement groups it should > > > create. Since cephfs metadata pools are usually very small, but have > > > many objects and high IO, the autoscaler gives them 4x the number of > > > placement groups that it would normally give for that amount of data. > > > > > ah ok, I understand. > > > > > So, your cephfs_data is set to a ratio of 0.9, and cephfs_metadata to > > > 0.3? Are the two pools using entirely different device classes, so > > > they are not sharing space? > > > > Yes, the metadata is on SSDs and the data on HDDs. > > > > > Anyway, I see that your overcommit is only "1.031x". So if you set > > > cephfs_data to 0.85, it should go away. > > > > This is not the case. I set the target_ratio to 0.7 and get this: > > > > POOL SIZE TARGET SIZE RATE RAW CAPACITY RATIO TARGET RATIO BIAS PG_NUM NEW PG_NUM AUTOSCALE > > cephfs_metadata 15736M 3.0 2454G 0.0188 0.3000 4.0 256 on > > cephfs_data 122.2T 1.5 165.4T 1.1085 0.7000 1.0 1024 on > > > > The ratio seems to have nothing to do with the target_ratio but the SIZE and the RAW_CAPACITY. > > Because the pool is still getting more data the SIZE increases and therefore the RATIO increases. > > The RATIO seems to be calculated by this formula > > RATIO = SIZE * RATE / RAW_CAPACITY. > > > > This is what I don't understand. The data in the cephfs_data pool seems to need more space than the raw capacity of the cluster provides. Hence the situation is called "overcommitment". > > > > But why is this only the case when the autoscaler is active? > > > > Thanks > > Lars > > > > > > > > On Thu, Oct 24, 2019 at 10:09 AM Lars Täuber <taeuber@xxxxxxx> wrote: > > > > > > > > Thanks Nathan for your answer, > > > > > > > > but I set the the Target Ratio to 0.9. It is the cephfs_data pool that makes the troubles. > > > > > > > > The 4.0 is the BIAS from the cephfs_metadata pool. This "BIAS" is not explained on the page linked below. So I don't know its meaning. > > > > > > > > How can be a pool overcommited when it is the only pool on a set of OSDs? > > > > > > > > Best regards, > > > > Lars > > > > > > > > Thu, 24 Oct 2019 09:39:51 -0400 > > > > Nathan Fish <lordcirth@xxxxxxxxx> ==> Lars Täuber <taeuber@xxxxxxx> : > > > > > The formatting is mangled on my phone, but if I am reading it correctly, > > > > > you have set Target Ratio to 4.0. This means you have told the balancer > > > > > that this pool will occupy 4x the space of your whole cluster, and to > > > > > optimize accordingly. This is naturally a problem. Setting it to 0 will > > > > > clear the setting and allow the autobalancer to work. > > > > > > > > > > On Thu., Oct. 24, 2019, 5:18 a.m. Lars Täuber, <taeuber@xxxxxxx> wrote: > > > > > > > > > > > This question is answered here: > > > > > > https://ceph.io/rados/new-in-nautilus-pg-merging-and-autotuning/ > > > > > > > > > > > > But it tells me that there is more data stored in the pool than the raw > > > > > > capacity provides (taking the replication factor RATE into account) hence > > > > > > the RATIO being above 1.0 . > > > > > > > > > > > > How comes this is the case? - Data is stored outside of the pool? > > > > > > How comes this is only the case when the autoscaler is active? > > > > > > > > > > > > Thanks > > > > > > Lars > > > > > > > > > > > > > > > > > > Thu, 24 Oct 2019 10:36:52 +0200 > > > > > > Lars Täuber <taeuber@xxxxxxx> ==> ceph-users@xxxxxxx : > > > > > > > My question requires too complex an answer. > > > > > > > So let me ask a simple question: > > > > > > > > > > > > > > What does the SIZE of "osd pool autoscale-status" tell/mean/comes from? > > > > > > > > > > > > > > Thanks > > > > > > > Lars > > > > > > > > > > > > > > Wed, 23 Oct 2019 14:28:10 +0200 > > > > > > > Lars Täuber <taeuber@xxxxxxx> ==> ceph-users@xxxxxxx : > > > > > > > > Hello everybody! > > > > > > > > > > > > > > > > What does this mean? > > > > > > > > > > > > > > > > health: HEALTH_WARN > > > > > > > > 1 subtrees have overcommitted pool target_size_bytes > > > > > > > > 1 subtrees have overcommitted pool target_size_ratio > > > > > > > > > > > > > > > > and what does it have to do with the autoscaler? > > > > > > > > When I deactivate the autoscaler the warning goes away. > > > > > > > > > > > > > > > > > > > > > > > > $ ceph osd pool autoscale-status > > > > > > > > POOL SIZE TARGET SIZE RATE RAW CAPACITY RATIO > > > > > > TARGET RATIO BIAS PG_NUM NEW PG_NUM AUTOSCALE > > > > > > > > cephfs_metadata 15106M 3.0 2454G 0.0180 > > > > > > 0.3000 4.0 256 on > > > > > > > > cephfs_data 113.6T 1.5 165.4T 1.0306 > > > > > > 0.9000 1.0 512 on > > > > > > > > > > > > > > > > > > > > > > > > $ ceph health detail > > > > > > > > HEALTH_WARN 1 subtrees have overcommitted pool target_size_bytes; 1 > > > > > > subtrees have overcommitted pool target_size_ratio > > > > > > > > POOL_TARGET_SIZE_BYTES_OVERCOMMITTED 1 subtrees have overcommitted > > > > > > pool target_size_bytes > > > > > > > > Pools ['cephfs_data'] overcommit available storage by 1.031x due > > > > > > to target_size_bytes 0 on pools [] > > > > > > > > POOL_TARGET_SIZE_RATIO_OVERCOMMITTED 1 subtrees have overcommitted > > > > > > pool target_size_ratio > > > > > > > > Pools ['cephfs_data'] overcommit available storage by 1.031x due > > > > > > to target_size_ratio 0.900 on pools ['cephfs_data'] > > > > > > > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > Lars _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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