Create a 3 Node Ceph Storage Cluster

Create a 3 Node Ceph Storage Cluster

Category : How-to

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ceph-logoCeph is an open source storage platform which is designed for modern storage needs. Ceph is scalable to the exabyte level and designed to have no single points of failure making it ideal for applications which require highly available flexible storage.

The below diagram shows the layout of an example 3 node cluster with Ceph storage. Two network interfaces can be used to increase bandwidth and redundancy. This can help to maintain sufficient bandwidth for storage requirements without affecting client applications.


This example will create a 3 node Ceph cluster with no single point of failure to provide highly redundant storage. I will refer to three host names which are all resolvable via my LAN DNS server; ceph1ceph2 and ceph3 which are all on the domain. Each of these nodes has two disks configured; one which runs the Linux OS and one which is going to be used for the Ceph storage. The below output shows the storage available, which is exactly the same on each host. /dev/vda is the root partition containing the OS install and /dev/vdb is an untouched partition which will be used for Ceph.

Before getting started with setting up the Ceph cluster, you need to do some preparation work. Make sure the following prerequisites are met before continuing the tutorial.

You will need to perform the following steps on all nodes in your Ceph cluster. First you will add the Ceph repositories and download the key to make the latest Ceph packages available. Add the following line to a new /etc/apt/sources.list.d/ file.

Add the below entry, save and close the file.

Download the key from Ceph’s git page and install it.

Update all local repository cache.

Note: if you see the below code when running apt-get update then the above wget command has failed – it could be because the Ceph git URL has changed.

Run the following commands on just one of your Ceph nodes. I’ll use ceph1 for this example. Update your local package cache and install the ceph-deploy command.

Create the first Ceph storage cluster and specify the first server in your cluster by either hostname or IP address for [SERVER].

For example

Now deploy Ceph onto all nodes which will be used for the Ceph storage.  Replace the below [SERVER] tags with the host name or IP address of your Ceph cluster including the host you are running the command on. See this post if you get a key error here.

For example

Install the Ceph monitor and accept the key warning as keys are generated. So that you don’t have a single point of failure, you will need at least 3 monitors. You must also have an uneven number of monitors – 3, 5, 7, etc. Again, you will need to replace the [SERVER] tags with your server names or IP addresses.


Now gather the keys of the deployed installation, just on your primary server.


It’s now time to start adding storage to the Ceph cluster. The fdisk output at the top of this page shows that the disk I’m going to use for Ceph is /dev/vdb, which is the same for all the nodes in my cluster. Using Ceph terminology, we will create an OSD based on each disk in the cluster. We could have used a file system location instead of a whole disk but, for this example, we will use a whole disk. Use the below command, changing [SERVER] to the name of the Ceph server which houses the disk and [DISK] to the disk representation in /dev/.

For example

If the command fails, it’s likely because you have partitions on your disk. Run the fdisk command on the disk and press d to delete the partitions and w to save the changes. For example:

Run the osd command for all nodes in your Ceph cluster

We now have to calculate the number of placement groups (PG) for our storage pool. A storage pool is a collection of OSDs, 3 in our case, which should each contain around 100 placement groups. Each placement group will hold your client data and map it to an OSD whilst providing redundancy to protect against disk failure.

To calculate your placement group count, multiply the amount of OSDs you have by 100 and divide it by the number of number of times each part of data is stored. The default is to store each part of data twice which means that if a disk fails, you won’t loose the data because it’s stored twice.

For our example,

3 OSDs * 100 = 300
Divided by replicas, 300 / 2 = 150

Now lets create the storage pool! Use the below command and substitute [NAME] with the name to give this storage pool and [PG] with the number we just calculated.

For example

You have now completed the set up for the Ceph storage pool. See my blog post on mounting Ceph storage on Proxmox.


Mario Kothe

31-Mar-2014 at 6:51 pm

wget -q -O- ‘;a=blob_plain;f=keys/release.asc’ | apt-key add –

This command does not work on a debian wheezy. Logged in as root.

The error reported is

gpg: no valid OpenPGP data found.


    31-Mar-2014 at 8:12 pm

    Hi Mario,

    It looks as though you have copied the text incorrectly. You are using in your wget command when you should be using . Please try again with the correct quotes.

Mario Kothe

31-Mar-2014 at 8:47 pm

Right. That was a copy paster error.

Having another problem now. I can not deploy the montior. Evertime I try

ceph-deploy –cluster domino mon create-initial domino-001

I get the following error. Using just create does not solve it either.
[domino-001][INFO ] Running command: sudo /usr/sbin/service ceph -c /etc/ceph/domino.conf start mon.domino-001
[domino-001][INFO ] Running command: sudo ceph –cluster=domino –admin-daemon /var/run/ceph/domino-mon.domino-001.asok mon_status
[domino-001][ERROR ] admin_socket: exception getting command descriptions: [Errno 2] No such file or directory

Mario Kothe

31-Mar-2014 at 8:49 pm

forget. may be the current complete config helps

fsid = xxxx [replaced]
mon_initial_members = domino-001
mon_host =
auth_cluster_required = cephx
auth_service_required = cephx
auth_client_required = cephx
filestore_xattr_use_omap = true
public network =
cluster network =

Mario Kothe

31-Mar-2014 at 9:42 pm

Is it possible that in the new release 0.72 is a bug. If I try the following:

ceph-deploy –cluster domino mon destroy

I get, what looks like seg faults:][WARNIN] 2014-03-31 23:42:18.115832 7f352fd56700 0 — :/1022380 >> pipe(0x16592a0 sd=3 :0 s=1 pgs=0 cs=0 l=1 c=0x1659500).fault
[][WARNIN] 2014-03-31 23:42:21.116229 7f352fc55700 0 — :/1022380 >> pipe(0x1657db0 sd=4 :0 s=1 pgs=0 cs=0 l=1 c=0x1658010).fault
[][WARNIN] 2014-03-31 23:42:24.116824 7f352fd56700 0 — :/1022380 >> pipe(0x165b4a0 sd=4 :0 s=1 pgs=0 cs=0 l=1 c=0x165b700).fault
[][WARNIN] 2014-03-31 23:42:27.117904 7f352fc55700 0 — :/1022380 >> pipe(0x16569b0 sd=4 :0 s=1 pgs=0 cs=0 l=1 c=0x1656c10).fault
[][WARNIN] 2014-03-31 23:42:30.119369 7f352fd56700 0 — :/1022380 >> pipe(0x7f3528000c90 sd=4 :0 s=1 pgs=0 cs=0 l=1 c=0x7f3528000ef0).fault
[][WARNIN] 2014-03-31 23:42:33.120081 7f352fc55700 0 — :/1022380 >> pipe(0x7f3528003010 sd=4 :0 s=1 pgs=0 cs=0 l=1 c=0x7f3528001dc0).fault
[][WARNIN] 2014-03-31 23:42:36.120654 7f352fd56700 0 — :/1022380 >> pipe(0x7f3528003620 sd=4 :0 s=1 pgs=0 cs=0 l=1 c=0x7f3528003880).fault
[][WARNIN] 2014-03-31 23:42:39.122456 7f352fc55700 0 — :/1022380 >> pipe(0x7f35280022f0 sd=4 :0 s=1 pgs=0 cs=0 l=1 c=0x7f3528002550).fault

Mario Kothe

31-Mar-2014 at 10:06 pm

Ok. purgedata and purge. After that clean install this time without a userdefined clustername. Looks like it works now. Up to the monitor part.


    1-Apr-2014 at 11:32 am

    I’m glad you got things going again.

Tawny Barnett

9-May-2014 at 8:28 pm

Hello James,

I’m using VM’s running ubuntu 12.04 to test this out and I’m getting the following error:

partition-guid=2:e618f906-4715-4a2e-9f22-9529061adb92′, ‘–typecode=2:45b0969e-9b03-4f30-b4c6-b4b80ceff106’, ‘–mbrtogpt’, ‘–‘, ‘/dev/sdb’]’ returned non-zero exit status 4
[ceph01][DEBUG ] ****************************************************************************
[ceph01][DEBUG ] Caution: Found protective or hybrid MBR and corrupt GPT. Using GPT, but disk
[ceph01][DEBUG ] verification and recovery are STRONGLY recommended.
[ceph01][DEBUG ] ****************************************************************************
[ceph01][DEBUG ] GPT data structures destroyed! You may now partition the disk using fdisk or
[ceph01][DEBUG ] other utilities.
[ceph01][DEBUG ] The operation has completed successfully.
[ceph01][DEBUG ] Information: Moved requested sector from 34 to 2048 in
[ceph01][DEBUG ] order to align on 2048-sector boundaries.
[ceph01][ERROR ] RuntimeError: command returned non-zero exit status: 1
[ceph_deploy.osd][ERROR ] Failed to execute command: ceph-disk-prepare –zap-disk –fs-type xfs –cluster ceph — /dev/sdb
[ceph_deploy][ERROR ] GenericError: Failed to create 1 OSDs

Can you please help?


19-Oct-2014 at 12:45 pm

I installed ceph two nodes, 2 mon 2 osd in xfs, also used the RBD and mount the pool on two different ceph host and when I write data through one of the hosts at the other I do not see the data, what’s wrong?


31-Oct-2014 at 10:35 am

Running command: ceph-deploy mon create ceph2 ceph3 results in the below erro:
[ceph-node3][ERROR ] admin_socket: exception getting command descriptions: [Errno 2] No such file or directory

But mon.ceph1 gets created with no errors. What could I be doing wrong


25-Nov-2014 at 6:59 pm

To Fix: [ceph-node3][ERROR ] admin_socket: exception getting command descriptions: [Errno 2] No such file or directory

Step 1:

You need to modify the ceph.conf file in the directory that you are running your ceph-deploy commands in.

add all your mon names nodes that you will be using in comma delimited format like this


(note: you can probably put hostnames in for mon_host argument instead of hard coded ip addresses but this worked for me… )

Step 2: then at the bottom of the ceph.conf file add a new argument/param specifying the public mask

public_network = ipaddress/mask (e.g

Step 3: save changes to the ceph.conf file

step 4: in the same directory this new modified ceph.conf file is in… run the following command

ceph-deploy –overwrite-conf mon create-initial

Conclusion: this will automatically create mon nodes on the hostnames/ipaddresses you specified and createa quorum amongst them… I hope this helps somebody else… took me hours to figure this out :(


12-Feb-2015 at 9:13 pm

First of all – thanks for this manual. Really helpfull!
But i have some unanswered questions about this setup:
1) is it possible in Ceph cluster to have OSD’s (/dev/vdb) with different sizes?!
2) what happens in this setup if i just shut down one of the servers and then turn it on again? What will happen to OSD’s and cluster?

Thanks a lot!



31-Mar-2016 at 3:54 am

If i have mon1, mon2, osd1,osd2,osd4,osd5, can i follow this tutorial? How to setup monitor so it can work properly? What is the step for my step?

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