How to use ceph to store large amount of small data - ceph

Question

I set up a cephfs cluster on my virtual machine, and then want to use this cluster to store a batch of image data (total 1.4G, each image is about 8KB). The cluster stores two copies, with a total of 12G of available space. But when I store data inside, the system prompts that the available space is insufficient. How to solve this?The details of the cluster are as follows:
Cluster Information:
cluster:
id: 891fb1a7-df35-48a1-9b5c-c21d768d129b
health: HEALTH_ERR
1 MDSs report slow metadata IOs
1 MDSs report slow requests
1 full osd(s)
1 nearfull osd(s)
2 pool(s) full
Degraded data redundancy: 46744/127654 objects degraded (36.618%), 204 pgs degraded
Degraded data redundancy (low space): 204 pgs recovery_toofull
too many PGs per OSD (256 > max 250)
clock skew detected on mon.node2, mon.node3
services:
mon: 3 daemons, quorum node1,node2,node3
mgr: node2(active), standbys: node1, node3
mds: cephfs-1/1/1 up {0=node1=up:active}, 2 up:standby
osd: 3 osds: 2 up, 2 in
data:
pools: 2 pools, 256 pgs
objects: 63.83k objects, 543MiB
usage: 10.6GiB used, 1.40GiB / 12GiB avail
pgs: 46744/127654 objects degraded (36.618%)
204 active+recovery_toofull+degraded
52 active+clean
Cephfs Space Usage:
[root#node1 0]# df -hT
文件系统 类型 容量 已用 可用 已用% 挂载点
/dev/mapper/nlas-root xfs 36G 22G 14G 62% /
devtmpfs devtmpfs 2.3G 0 2.3G 0% /dev
tmpfs tmpfs 2.3G 0 2.3G 0%
/dev/shm
tmpfs tmpfs 2.3G 8.7M 2.3G 1% /run
tmpfs tmpfs 2.3G 0 2.3G 0%
/sys/fs/cgroup
/dev/sda1 xfs 1014M 178M 837M 18% /boot
tmpfs tmpfs 2.3G 28K 2.3G 1%
/var/lib/ceph/osd/ceph-0
tmpfs tmpfs 471M 0 471M 0%
/run/user/0
192.168.152.3:6789,192.168.152.4:6789,192.168.152.5:6789:/ ceph 12G 11G 1.5G 89% /mnt/test
Ceph OSD:
[root#node1 mnt]# ceph osd pool ls
cephfs_data
cephfs_metadata
[root#node1 mnt]# ceph osd pool get cephfs_data size
size: 2
[root#node1 mnt]# ceph osd pool get cephfs_metadata size
size: 2
ceph.dir.layout:
[root#node1 mnt]# getfattr -n ceph.dir.layout /mnt/test
getfattr: Removing leading '/' from absolute path names
# file: mnt/test
ceph.dir.layout="stripe_unit=65536 stripe_count=1 object_size=4194304 pool=cephfs_data"

Answer 1

Storing small files, you need to watch the minimum allocation size. Until the Nautilus release, this defaulted to 16k for SSD and 64k for HDD, but with the new Ceph Pacific the default minimum allocation has been tuned to 4k for both.
I suggest you use Pacific, or manually tune Octopus to the same numbers if that's the version you installed.
You also want to use replication (as opposed to Erasure Coding) if your files are under a multiple of the minimum allocation size, as the chunks of EC would use the same minimum allocation and will waste slack space otherwise. You already made the right choice here by using replication, I am just mentioning it here because you may be tempted by EC's touted space-saving properties -- which unfortunately do not apply to small files.

Answer 2

you need to set bluestore_min_alloc_size to 4096 by default its value is 64kb
[osd]
bluestore_min_alloc_size = 4096
bluestore_min_alloc_size_hdd = 4096
bluestore_min_alloc_size_ssd = 4096