We are running a three-node Ceph cluster on riboflavin, ginkgo and biloba for the purpose of cloud storage. Most Ceph services are running on riboflavin or ginkgo; biloba is just providing a tiny bit of extra storage space.
Official documentation: https://docs.ceph.com/en/latest/
At the time this page was written, the latest version of Ceph was 'Pacific'; check the website above to see what the latest version is.
The instructions below were adapted from https://docs.ceph.com/en/pacific/cephadm/install/.
riboflavin was used as the bootstrap host, since it has the most storage.
Add the following to /etc/apt/sources.list.d/ceph.list:
deb http://mirror.csclub.uwaterloo.ca/ceph/debian-pacific/ bullseye main
Download the Ceph release key for the Debian packages:
wget -O /etc/apt/trusted.gpg.d/ceph.release.gpg https://download.ceph.com/keys/release.gpg
apt update apt install cephadm podman ceph boostrap --mon-ip 172.19.168.25
For the rest of the instructions below, the
ceph command can be run inside a Podman container by running
cephadm shell. Alternatively, you can install the
ceph-common package to run
ceph directly on the host.
Add the disks for riboflavin:
ceph orch daemon add osd riboflavin:/dev/sdb ceph orch daemon add osd riboflavin:/dev/sdc
Note: Unfortunately Ceph didn't like it when I used one of the /dev/disk/by-id paths, so I had to use the /dev/sdX paths instead. I'm not sure what'll happen if the device names change at boot. Let's just cross our fingers and pray.
Add more hosts:
ceph orch host add ginkgo 172.19.168.22 --labels _admin ceph orch host add biloba 172.19.168.23
Add each available disk on each of the additional hosts.
Disable unnecessary services:
ceph orch rm alertmanager ceph orch rm grafana ceph orch rm node-exporter
Set the autoscale profile to scale-up instead of scale-down:
ceph osd pool set autoscale-profile scale-up
Set the default pool replication factor to 2 instead of 3:
ceph config set global osd_pool_default_size 2
Deploy the Managers and Monitors on riboflavin and ginkgo only:
ceph orch apply mon --placement '2 riboflavin ginkgo' ceph orch apply mgr --placement '2 riboflavin ginkgo'
CloudStack Primary Storage
We are using RBD (RADOS Block Device) for CloudStack primary storage. The instructions below were adapted from https://docs.ceph.com/en/pacific/rbd/rbd-cloudstack/.
Create and initialize a pool:
ceph osd pool create cloudstack rbd pool init cloudstack
Create a user for CloudStack:
ceph auth get-or-create client.cloudstack mon 'profile rbd' osd 'profile rbd pool=cloudstack'
Make a backup of this key. There is currently a copy in /etc/ceph/ceph.client.cloudstack.keyring on biloba. If you want to use the
ceph command with this set of credentials, use the
-n flag, e.g.
ceph -n client.cloudstack status
Here are some RBD commands which might be useful:
List images (i.e. block devices) in the cloudstack pool:
rbd ls -p cloudstack
View snapshots for an image:
rbd snap ls cloudstack/265dc008-4db5-11ec-b585-32ee6075b19b
Unprotect a snapshot:
rbd snap unprotect cloudstack/265dc008-4db5-11ec-b585-32ee6075b19b@cloudstack-base-snap
Purge all snapshots for an image (after unprotecting them):
rbd snap purge cloudstack/265dc008-4db5-11ec-b585-32ee6075b19b
Delete an image:
rbd rm cloudstack/265dc008-4db5-11ec-b585-32ee6075b19b
A quick 'n dirty script to delete all images in the pool:
rbd ls -p cloudstack | while read image; do rbd snap unprotect cloudstack/$image@cloudstack-base-snap; done rbd ls -p cloudstack | while read image; do rbd snap purge cloudstack/$image; done rbd ls -p cloudstack | while read image; do rbd rm cloudstack/$image; done
CloudStack Secondary Storage
We are using NFS (v4) for CloudStack secondary storage. The steps below were adapted from:
Create a new CephFS filesystem:
ceph fs volume create cloudstack-secondary
Enable the NFS module:
ceph mgr module enable nfs
Create a cluster placed on two hosts:
ceph nfs cluster create cloudstack-nfs --placement '2 riboflavin ginkgo'
View cluster info:
ceph nfs cluster ls ceph nfs cluster info cloudstack-nfs
Now create a CephFS export:
ceph nfs export create cephfs cloudstack-secondary cloudstack-nfs /cloudstack-secondary /
View export info:
ceph nfs export ls cloudstack-nfs ceph nfs export get cloudstack-nfs /cloudstack-secondary
Now on the clients, we can just mount the NFS export normally:
mkdir /mnt/cloudstack-secondary mount -t nfs4 -o port=2049 ceph-nfs.cloud.csclub.uwaterloo.ca:/cloudstack-secondary /mnt/cloudstack-secondary
The NFS module in Ceph is just NFS-Ganesha, which does theoretically support ACLs, but I wasn't able to get it to work. I kept on getting some weird Python error. So we're going to use our iptables-fu instead (on riboflavin and ginkgo; make sure iptables-persistent is installed):
iptables -N CEPH-NFS iptables -A INPUT -j CEPH-NFS iptables -A CEPH-NFS -s 172.19.168.0/27 -j RETURN iptables -A CEPH-NFS -p tcp --dport 2049 -j REJECT iptables -A CEPH-NFS -p udp --dport 2049 -j REJECT iptables-save > /etc/iptables/rules.v4 ip6tables -N CEPH-NFS ip6tables -A INPUT -j CEPH-NFS ip6tables -A CEPH-NFS -s fd74:6b6a:8eca:4902::/64 -j RETURN ip6tables -A CEPH-NFS -p tcp --dport 2049 -j REJECT ip6tables -A CEPH-NFS -p udp --dport 2049 -j REJECT ip6tables-save > /etc/iptables/rules.v6
There is a web dashboard for Ceph running on riboflavin which is useful to get a holistic view of the system. You will need to do a port-forward over SSH:
ssh -L 8443:172.19.168.25:8443 riboflavin
Now if you visit https://localhost:8443 (ignore the HTTPS warning), you can login to the dashboard. Credentials are stored in the usual place.
Adding a new disk
Let's say we added a new disk /dev/sdg to ginkgo. Log in to one of the Ceph management servers (riboflavin or ginkgo), then run
# clear any metadata at the start of the disk dd if=/dev/zero of=/dev/sdg bs=1M count=10 conv=fsync # Run this from inside `cephadm shell` ceph orch daemon add osd ginkgo:/dev/sdg
And that's it! You can run
ceph status to see the progress of the PGs getting rebalanced.
Recovering from a disk failure
Check which placement group(s) failed:
# Run this from `cephadm shell` ceph health detail
The output will look something like this:
HEALTH_ERR 1 scrub errors; Possible data damage: 1 pg inconsistent [ERR] OSD_SCRUB_ERRORS: 1 scrub errors [ERR] PG_DAMAGED: Possible data damage: 1 pg inconsistent pg 2.5 is active+clean+inconsistent, acting [3,0]
This means that placement group 2.5 failed and is in OSDs 3 and 0. Since our cluster has a replication factor of 2, one of those OSDs will be on the machine with the failed disk, and the other OSD will be on a healthy machine. Run this to see which machines have which OSDs:
ceph osd tree
Repairing the placement group
If the disk failure might have been intermittent, try and see if we can repair the PG first. See https://docs.ceph.com/en/pacific/rados/operations/pg-repair/ for details.
Removing or replacing a disk
First, find the OSD corresponding to the failed disk:
# Run this from `cephadm shell` ceph-volume lvm list
Read these pages:
Here's the TLDR (assuming OSD 3 has the disk which failed):
First, take the OSD out of the cluster:
ceph osd out osd.3
Wait until the data is backfilled to the other OSDs (this could take a long time):
Remove the OSD daemon, then purge the OSD completely:
ceph orch daemon rm osd.3 --force ceph osd purge osd.3 --yes-i-really-mean-it
Destroy the LVM logical volume and volume group:
ceph-volume lvm zap --destroy --osd-id 3
At this point, the hard drive can be removed.
After the drive has been replaced, zap it and add it to the cluster normally:
dd if=/dev/zero of=/dev/sde bs=1M count=10 conv=fsync ceph orch daemon add osd ginkgo:/dev/sde
Reducing log verbosity
By default, debug messages are enabled and written to stderr (so they up in the journald logs because they run in Podman). Unfortunately there is a bug in Ceph which seems to always cause debug messages to be enabled on stderr specifically. So we will log to syslog instead (which is just systemd-journald on Debian).
cephadm shell on riboflavin, then run the following:
ceph config set global mon_cluster_log_file_level info ceph config set global log_to_stderr false ceph config set global mon_cluster_log_to_stderr false ceph config set global mon_cluster_log_to_syslog true
These setting should take effect on all of the Ceph hosts immediately. See https://docs.ceph.com/en/pacific/rados/configuration/ceph-conf/ for reference.
Here are some commands which may be useful. See the man page for a full reference.
ceph orch device ls
Note: this doesn't actually show all of the individual disks. I think it might have to do with the hardware RAID controllers.
Show OSDs (Object Storage Daemons) on the current host (this needs to be run from
ceph-volume lvm list
ceph orch ls
Show daemons of those services:
ceph orch ps
Show non-default config settings:
ceph config dump
ceph osd pool ls detail
ceph auth ls