I am using ceph version 13.2.6 (mimic) on test setup trying with cephfs.

My current setup:

3 nodes, 1 node contain two bricks and other 2 nodes contain single brick each.

Volume is a 3 replica, I am trying to simulate node failure.

I powered down one host and started getting msg in other systems when running any command
"-bash: fork: Cannot allocate memory" and system not responding to commands.

what could be the reason for this?

at this stage, I could able to read some of the data stored in the volume and some just waiting for IO.

output from "sudo ceph -s"
  cluster:
    id:     7c138e13-7b98-4309-b591-d4091a1742b4
    health: HEALTH_WARN
            1 osds down
            2 hosts (3 osds) down
            Degraded data redundancy: 5313488/7970232 objects degraded (66.667%), 64 pgs degraded

  services:
    mon: 1 daemons, quorum mon01
    mgr: mon01(active)
    mds: cephfs-tst-1/1/1 up  {0=mon01=up:active}
    osd: 4 osds: 1 up, 2 in

  data:
    pools:   2 pools, 64 pgs
    objects: 2.66 M objects, 206 GiB
    usage:   421 GiB used, 3.2 TiB / 3.6 TiB avail
    pgs:     5313488/7970232 objects degraded (66.667%)
             64 active+undersized+degraded

  io:
    client:   79 MiB/s rd, 24 op/s rd, 0 op/s wr

output from : sudo ceph osd df
ID CLASS WEIGHT  REWEIGHT SIZE    USE     AVAIL   %USE  VAR  PGS
 0   hdd 1.81940        0     0 B     0 B     0 B     0    0   0
 3   hdd 1.81940        0     0 B     0 B     0 B     0    0   0
 1   hdd 1.81940  1.00000 1.8 TiB 211 GiB 1.6 TiB 11.34 1.00   0
 2   hdd 1.81940  1.00000 1.8 TiB 210 GiB 1.6 TiB 11.28 1.00  64
                    TOTAL 3.6 TiB 421 GiB 3.2 TiB 11.31
MIN/MAX VAR: 1.00/1.00  STDDEV: 0.03

regards

Amudhan