Hi,

I have a cephfs cluster as follows:

1 15x HDD data pool (primary cephfs data pool)
1 2x SSD data pool (linked to a specific dir via xattrs)
1 2x SSD metadata pool
1 2x SSD cache tier pool

the cache tier pool consists in 2 host, with one SSD OSD on each host, with
size=2 replicated by host.
Last night the disks went 100% full and the cluster went down.

I know I made a mistake and set target_max_objects and target_max_bytes to
0 in the cache pool,
but isn't ceph supposed to stop writing to an OSD when it reaches
it's full_ratio (default 0.95) ?
And what about the cache_target_full_ratio in the cache tier pool?

Here is the cluster:

~# ceph fs ls
name: cephfs, metadata pool: cephfs_metadata, data pools: [cephfs_data
cephfs_data_ssd ]

* the Metadata and the SSD data pools use the same 2 OSDs (one cephfs
directory is linked to the SSD data pool via xattrs)

~# ceph -v
ceph version 10.2.9-4-gbeaec39 (beaec397f00491079cd74f7b9e3e10660859e26b)

~# ceph osd pool ls detail
pool 1 'cephfs_data' replicated size 3 min_size 2 crush_ruleset 0
object_hash rjenkins pg_num 1024 pgp_num 1024 last_change 136 lfor 115
flags hashpspool crash_replay_interval 45 tiers 3 read_tier 3 write_tier 3
stripe_width 0
pool 2 'cephfs_metadata' replicated size 2 min_size 1 crush_ruleset 2
object_hash rjenkins pg_num 128 pgp_num 128 last_change 617 flags
hashpspool stripe_width 0
pool 3 'cephfs_cache' replicated size 2 min_size 1 crush_ruleset 1
object_hash rjenkins pg_num 128 pgp_num 128 last_change 1493 lfor 115 flags
hashpspool,incomplete_clones tier_of 1 cache_mode writeback target_bytes
343597383680 hit_set bloom{false_positive_probability: 0.05, target_size:
0, seed: 0} 0s x0 decay_rate 0 search_last_n 0 stripe_width 0
pool 12 'cephfs_data_ssd' replicated size 2 min_size 1 crush_ruleset 2
object_hash rjenkins pg_num 128 pgp_num 128 last_change 653 flags
hashpspool stripe_width 0

~# ceph osd tree
ID  WEIGHT   TYPE NAME                      UP/DOWN REWEIGHT
PRIMARY-AFFINITY
 -8  0.17598 root default-ssd

 -9  0.09299     host bhs1-mail03-fe01-data

 17  0.09299         osd.17                      up  1.00000
 1.00000
-10  0.08299     host bhs1-mail03-fe02-data

 18  0.08299         osd.18                      up  1.00000
 1.00000
 -7  0.86319 root cache-ssd

 -5  0.43159     host bhs1-mail03-fe01

 15  0.43159         osd.15                      up  1.00000
 1.00000
 -6  0.43159     host bhs1-mail03-fe02

 16  0.43159         osd.16                      up  1.00000
 1.00000
 -1 79.95895 root default

 -2 26.65298     host bhs1-mail03-ds01

  0  5.33060         osd.0                       up  1.00000
 1.00000
  1  5.33060         osd.1                       up  1.00000
 1.00000
  2  5.33060         osd.2                       up  1.00000
 1.00000
  3  5.33060         osd.3                       up  1.00000
 1.00000
  4  5.33060         osd.4                       up  1.00000
 1.00000
 -3 26.65298     host bhs1-mail03-ds02

  5  5.33060         osd.5                       up  1.00000
 1.00000
  6  5.33060         osd.6                       up  1.00000
 1.00000
  7  5.33060         osd.7                       up  1.00000
 1.00000
  8  5.33060         osd.8                       up  1.00000
 1.00000
  9  5.33060         osd.9                       up  1.00000
 1.00000
 -4 26.65298     host bhs1-mail03-ds03

 10  5.33060         osd.10                      up  1.00000
 1.00000
 12  5.33060         osd.12                      up  1.00000
 1.00000
 13  5.33060         osd.13                      up  1.00000
 1.00000
 14  5.33060         osd.14                      up  1.00000
 1.00000
 19  5.33060         osd.19                      up  1.00000
 1.00000

~# ceph osd crush rule dump
[
    {
        "rule_id": 0,
        "rule_name": "replicated_ruleset",
        "ruleset": 0,
        "type": 1,
        "min_size": 1,
        "max_size": 10,
        "steps": [
            {
                "op": "take",
                "item": -1,
                "item_name": "default"
            },
            {
                "op": "chooseleaf_firstn",
                "num": 0,
                "type": "host"
            },
            {
                "op": "emit"
            }
        ]
    },
    {
        "rule_id": 1,
        "rule_name": "replicated_ruleset_ssd",
        "ruleset": 1,
        "type": 1,
        "min_size": 1,
        "max_size": 10,
        "steps": [
            {
                "op": "take",
                "item": -7,
                "item_name": "cache-ssd"
            },
            {
                "op": "chooseleaf_firstn",
                "num": 0,
                "type": "host"
            },
            {
                "op": "emit"
            }
        ]
    },
    {
        "rule_id": 2,
        "rule_name": "replicated-data-ssd",
        "ruleset": 2,
        "type": 1,
        "min_size": 1,
        "max_size": 10,
        "steps": [
            {
                "op": "take",
                "item": -8,
                "item_name": "default-ssd"
            },
            {
                "op": "chooseleaf_firstn",
                "num": 0,
                "type": "host"
            },
            {
                "op": "emit"
            }
        ]
    }
]

~# ceph osd pool get cephfs_cache all
size: 2
min_size: 1
crash_replay_interval: 0
pg_num: 128
pgp_num: 128
crush_ruleset: 1
hashpspool: true
nodelete: false
nopgchange: false
nosizechange: false
write_fadvise_dontneed: false
noscrub: false
nodeep-scrub: false
hit_set_type: bloom
hit_set_period: 0
hit_set_count: 0
hit_set_fpp: 0.05
use_gmt_hitset: 1
auid: 0
target_max_objects: 0
target_max_bytes: 343597383680
cache_target_dirty_ratio: 0.5
cache_target_dirty_high_ratio: 0.7
cache_target_full_ratio: 0.8
cache_min_flush_age: 3600
cache_min_evict_age: 3600
min_read_recency_for_promote: 0
min_write_recency_for_promote: 0
fast_read: 0
hit_set_grade_decay_rate: 0
hit_set_search_last_n: 0


Regards,

Webert Lima
DevOps Engineer at MAV Tecnologia
*Belo Horizonte - Brasil*
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