Monday, September 29, 2014

What Is GlusterFS Filesystem and How Does It Configure In Linux?

Hello everybody,

Today, I would like to talk about GlusterFS in Linux. Note: It’s Gluster and not Cluster. Glusterfs is a distributed file system and it’s very flexible. You can claim free spaces on each server and make it a huge virtual drive for clients. It’s flexible because you can add/remove servers and make it bigger or smaller size and also you can configure it on tcp protocol for remote access. It reminds me Cloud or Raid but much more flexible.  It’s fast too and most importantly, it’s easy administration. It has ability to balance the data and workload and also high available. It’s really cool. And yes, it’s Open Source

Here, I am demonstrating it with 4 CentOS 7.0 machines. 3 servers and 1 client.
At the moment that I am writing this blog, the latest version is Glusterfs 3.5.2. I am going to download the package and install it manually, however, you can install it with yum command easily. The only thing is that yum repository is not up-to-date and you may end up with lower version of Glusterfs such as 3.4.0 or something like that, but installation is much easier. I am going to install it manually for demonstration purposes.

To download and install GlusterFS, run the following commands as a root user on each server and also client:


yum install gcc git nfs-utils perl rpcbind
yum install gcc git nfs-utils perl rpcbind
yum install rsyslog-mmjsonparse
yum install libibverbs
yum install librdmacm
rpm -Uvh glusterfs-3.5.2-1.el7.x86_64.rpm glusterfs-api-3.5.2-1.el7.x86_64.rpm glusterfs-api-devel-3.5.2-1.el7.x86_64.rpm glusterfs-cli-3.5.2-1.el7.x86_64.rpm glusterfs-debuginfo-3.5.2-1.el7.x86_64.rpm glusterfs-devel-3.5.2-1.el7.x86_64.rpm glusterfs-extra-xlators-3.5.2-1.el7.x86_64.rpm glusterfs-fuse-3.5.2-1.el7.x86_64.rpm glusterfs-geo-replication-3.5.2-1.el7.x86_64.rpm glusterfs-libs-3.5.2-1.el7.x86_64.rpm glusterfs-rdma-3.5.2-1.el7.x86_64.rpm glusterfs-server-3.5.2-1.el7.x86_64.rpm

                                                                           Figure 1  

After completing installation, run the following command and find out the version. Note: It’s under GNU license:
glusterfs –V

                                                                           Figure 2

Now, you need to open firewall. Run the below commands in all machines:
iptables -I INPUT -m state --state NEW -m tcp -p tcp --dport 24007:24011 -j ACCEPT
iptables -I INPUT -m state --state NEW -m tcp -p tcp --dport 111 -j ACCEPT
iptables -I INPUT -m state --state NEW -m udp -p udp --dport 111 -j ACCEPT

If you need to add more servers, you must add more port to open in firewall for each server. For example, 24012, 24013, … in this case.

Now, it’s time to start the glusterd service:
service glusterd start
/bin/systemctl start glusterd.service

                                                                           Figure 3

Now, we need to configure our servers. You must select one of this servers, doesn’t matter which one, to act as a master server. The first thing that you need to do is creating a Pool or Storage Pool. Log in as a root user in master server and run the following commands:
service glusterd  restart
gluster peer probe
gluster peer probe

You must replace the IPs above with your IP addresses. You don’t need to restart you glusterd service, but if you get “Connection failed. Please check if gluster daemon is operational” message like me as showed in figure 4, just restart glusterd service and then you should be fine.

                                                                            Figure 4

To see what’s going on, run this command:

gluster peer status

                                                                                 Figure 5
Now, it’s time to create a volume or a virtual volume in other words. I call it a virtual volume because client only sees one volume or disk drive, however, this volume or disk resides on all servers or 3 servers in this case. Anyway, create an empty directory on each server:
mkdir –p /mnt/storage.132
mkdir –p /mnt/storage.133
mkdir –p /mnt/storage.134

Then, on master server, run the below command to create a volume:

gluster volume create MyCorpVol transport tcp force

I used “force” option because it kept warning me that it’s not a good idea to install on root directory or get space from system partition; but since it’s for training purposes, I just force it. Ideally, you must install it on a separate disk, anything other than system partition. See Figure 6.

OH! By the way, we have 3 types of volume:
  1.  Distributed volume (command above).
Distributed volume distributes files to all servers (like Load Balancer) and because it balances the load, there is no pressure on one server and read/write files are fast. However, this is no fault tolerance. It means if one of servers goes down, you are going to lose your part of data that resides on that particular server. 

     2.  Replicated volume (see below).
Replicated volume writes files to all servers (replica) and you have fault tolerance now, however, the speed of writing files is going to be slow. The good thing is that you can define peer of replica. For example, if you have 4 servers, you can define 2 replicas. So, in that way, you have both fault tolerance and speed.

3        3.   Distributed Strip volume.

This is going to be very fast because gluster divides files to equal pieces and writes them to all servers at the same time. Therefore, it’s so fast. However, there is no fault tolerance.

Now, it’s time to “start” our created volume. Run the command below:

gluster volume start MyCorpVol

To see the volume’s info, run this command:

gluster volume info

                                                                           Figure 6

On client side, first we need to mount our created volume. Run the bellow command to mount it:

mkdir –p /opt/CorpStorage
mount –t glusterfs /opt/CorpStorage

and yes; of course you can add it to /etc/fstab to mount it automatically after reboot. Now, let’s try it and see how it works. I am going to copy some files to mounted folder. Figure 7.

                                                                              Figure 7
Do you want to know where those files actually have gone? Look at Figure 8, 9, and 10. Note: In this example, it’s Distribute Volume. It randomly distributes files. At this example, server 134 is empty, but it may get some files next time as files distributes to all servers.

                                                                              Figure 8
                                                                             Figure 9
                                                                              Figure 10  

Let’s create another volume with replicated mode. Run the following commands:

gluster volume create MyCorpVol2 replica 3 transport tcp force

gluster volume start MyCorpVol2

gluster volume info

                                                                        Figure 11   

The same deal here on the client side:

mkdir –p /opt/CorpStorage2
mount –t glusterfs /opt/CorpStorage2

Now, if you copy some files on mounted directory, you should be able to see all files on all servers because the type of volume is Replicated Volume. See Figure 12, 13, 14 and 15.

                                                                             Figure 12
                                                                             Figure 13
                                                                             Figure 14
                                                                             Figure 15

When you want to add more storages (it can be on the same servers or a new server), you need to add bricks to existing volume. Run the following commands:

 mkdir –p /var/storage4
 gluster volume add-brick MyCorpVol2 replica 4 force

                                                                            Figure 16 

To reduce the size of volume, you need to remove-brick command:

gluster volume remove-brick MyCorpVol2 replica 3 force

                                                                                Figure 17 

In this example, because we are using Replication Volume, you don’t need to rebalance data and it will copy all data as soon as next file comes in to all servers. However, if you are using Distributed or Strip Volume, you need to rebalance data. Let’s try another example:

In this example, there are 2 Distributed volumes and I want to add one more volume and then rebalance data on servers. Run the following commands:

gluster peer probe    ---> to add new server to storage pool
gluster volume add-brick MyCorpVol3 force
gluster volume rebalance MyCorpVol3 start
gluster volume rebalance MyCorpVol3 status  ---> to see the status of volume

                                                                               Figure 19

The same deal here when you want to remove a brick:

gluster volume remove-brick MyCorpVol3 force
gluster volume rebalance MyCorpVol3 start
gluster volume rebalance MyCorpVol3 status

                                                                               Figure 20

To monitor your volumes and servers run the below command:

gluster volume profile MyCorpVol3  info

                                                                       Figure 21 
If you want to grant or deny access to a glusterfs volume for a specific client or subnet, use the following commands but replace the ip or hostname with your ip or hostname.

gluster volume set MyCorpVol3  auth.allow (IP)
gluster volume set MyCorpVol3 auth.reject (IP)

                                                                        Figure 22
And finally, if you want to delete an existing volume, you must first stop the volume and then delete it:

gluster volume stop MyCorpVol3
gluster volume delete MyCorpVol3

That’s all. I hope you enjoyed of reading this blog. Don’t forget to put your comments here.
Khosro Taraghi