HEALTH_WARN too few PGs per OSD (21 < min 30）解决方法

标签（空格分隔）： ceph，ceph运维，pg

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集群环境：

[root@node3 ~]# cat /etc/redhat-release 
CentOS Linux release 7.3.1611 (Core) 
[root@node3 ~]# ceph -v
ceph version 12.2.1 (3e7492b9ada8bdc9a5cd0feafd42fbca27f9c38e) luminous (stable)

集群当前布局：

[root@node3 ceph-6]# ceph osd tree
ID CLASS WEIGHT  TYPE NAME      STATUS REWEIGHT PRI-AFF 
-1       0.08844 root default                           
-3       0.02948     host node1                         
 0   hdd 0.00980         osd.0      up  1.00000 1.00000 
 3   hdd 0.00980         osd.3      up  1.00000 1.00000 
-5       0.02948     host node2                         
 1   hdd 0.00980         osd.1      up  1.00000 1.00000 
 4   hdd 0.00980         osd.4      up  1.00000 1.00000 
-7       0.02948     host node3                         
 2   hdd 0.00980         osd.2      up  1.00000 1.00000 
 5   hdd 0.00980         osd.5      up  1.00000 1.00000 

为每个主机再添加一个osd：

为了重现too few pgs的错误，同时为了创建指定数据位置osd，下面创建bluestore的osd，数据存储在/dev/sdd1上。在每个主机上执行下面的步骤：

第一步：创建bluestore类型的osd：

[root@node2 ~]# ceph-disk prepare --bluestore /dev/sdd2 --block.db /dev/sdd1
set_data_partition: incorrect partition UUID: cafecafe-9b03-4f30-b4c6-b4b80ceff106, expected ['4fbd7e29-9d25-41b8-afd0-5ec00ceff05d', '4fbd7e29-9d25-41b8-afd0-062c0ceff05d', '4fbd7e29-8ae0-4982-bf9d-5a8d867af560', '4fbd7e29-9d25-41b8-afd0-35865ceff05d']
prepare_device: OSD will not be hot-swappable if block.db is not the same device as the osd data
prepare_device: Block.db /dev/sdd1 was not prepared with ceph-disk. Symlinking directly.
meta-data=/dev/sdd2              isize=2048   agcount=4, agsize=648895 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=2595579, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

第二步：激活该osd：

[root@node2 ~]# ceph-disk activate /dev/sdd2
creating /var/lib/ceph/tmp/mnt.mR3qCJ/keyring
added entity osd.8 auth auth(auid = 18446744073709551615 key=AQBNqOVZt/iUBBAArkrWrZi9N0zxhHhYfhanyw== with 0 caps)
got monmap epoch 1
Removed symlink /etc/systemd/system/ceph-osd.target.wants/ceph-osd@8.service.
Created symlink from /etc/systemd/system/ceph-osd.target.wants/ceph-osd@8.service to /usr/lib/systemd/system/ceph-osd@.service.

最后查看集群布局，发现共有9个osd：

[root@node3 ~]# ceph osd tree
ID CLASS WEIGHT  TYPE NAME      STATUS REWEIGHT PRI-AFF 
-1       0.08844 root default                           
-3       0.02948     host node1                         
 0   hdd 0.00980         osd.0      up  1.00000 1.00000 
 3   hdd 0.00980         osd.3      up  1.00000 1.00000 
 7   hdd 0.00989         osd.7      up  1.00000 1.00000 
-5       0.02948     host node2                         
 1   hdd 0.00980         osd.1      up  1.00000 1.00000 
 4   hdd 0.00980         osd.4      up  1.00000 1.00000 
 8   hdd 0.00989         osd.8      up  1.00000 1.00000 
-7       0.02948     host node3                         
 2   hdd 0.00980         osd.2      up  1.00000 1.00000 
 5   hdd 0.00980         osd.5      up  1.00000 1.00000 
 6   hdd 0.00989         osd.6      up  1.00000 1.00000 

重现too few pgs错误：

创建一个pg数较小的存储池：

[root@node3 ~]# ceph osd pool create rbd 64 64 
pool 'rbd' created
[root@node3 ~]# rados lspools
rbd
[root@node3 ~]# ceph -s
  cluster:
    id:     b8b4aa68-d825-43e9-a60a-781c92fec20e
    health: HEALTH_WARN
            too few PGs per OSD (21 < min 30)
 
  services:
    mon: 1 daemons, quorum node1
    mgr: node1(active)
    osd: 9 osds: 9 up, 9 in
 
  data:
    pools:   1 pools, 64 pgs
    objects: 0 objects, 0 bytes
    usage:   9742 MB used, 82717 MB / 92459 MB avail
    pgs:     64 active+clean

从上面可以看到，提示说每个osd上的pg数量小于最小的数目30个。pgs为64，因为是3副本的配置，所以当有9个osd的时候，每个osd上均分了64/9 *3=21个pgs,也就是出现了如上的错误 小于最小配置30个。

集群这种状态如果进行数据的存储和操作，会发现集群卡死，无法响应io，同时会导致大面积的osd down。

解决办法：修改默认pool rbd的pgs

[root@node3 ~]# ceph osd pool set rbd pg_num 128
set pool 1 pg_num to 128

之后查看集群状态

[root@node3 ~]# ceph -s
  cluster:
    id:     b8b4aa68-d825-43e9-a60a-781c92fec20e
    health: HEALTH_WARN
            Reduced data availability: 5 pgs inactive, 44 pgs peering
            Degraded data redundancy: 49 pgs unclean
            1 pools have pg_num > pgp_num
 
  services:
    mon: 1 daemons, quorum node1
    mgr: node1(active)
    osd: 9 osds: 9 up, 9 in
 
  data:
    pools:   1 pools, 128 pgs
    objects: 0 objects, 0 bytes
    usage:   9743 MB used, 82716 MB / 92459 MB avail
    pgs:     7.031% pgs unknown
             38.281% pgs not active
             70 active+clean
             44 peering
             9  unknown
             5  activating

可以看到还没ok，提示pg_num 大于 pgp_num，所以还需要修改pgp_num

[root@node3 ~]# ceph osd pool set rbd pgp_num 128
set pool 1 pgp_num to 128

再次查看集群状态：

[root@node3 ~]# ceph -s
  cluster:
    id:     b8b4aa68-d825-43e9-a60a-781c92fec20e
    health: HEALTH_OK
 
  services:
    mon: 1 daemons, quorum node1
    mgr: node1(active)
    osd: 9 osds: 9 up, 9 in
 
  data:
    pools:   1 pools, 128 pgs
    objects: 0 objects, 0 bytes
    usage:   9750 MB used, 82709 MB / 92459 MB avail
    pgs:     128 active+clean

这里是简单的实验，pool上也没有数据，所以修改pg影响并不大，但是如果是生产环境，这时候再重新修改pg数，会对生产环境产生较大影响。因为pg数变了，就会导致整个集群的数据重新均衡和迁移，数据越大响应io的时间会越长。所以，最好在一开始就设置好pg数。

参考资料：

HEALTH_WARN too few PGs per OSD (16 < min 30）