Basic guide to deploying a simple three-node Lustre cluster on Centos 7.  

Updated fork of [joshuar/Three-Node-LustreFS-Cluster-Quickstart.md](https://gist.github.com/joshuar/4e283308c932ec62fc05), which was based on Intel's [How to Create and Mount a Lustre Filesystem](https://wiki.hpdd.intel.com/display/PUB/Create+and+Mount+a+Lustre+Filesystem).  

## Overview

(Note: I am a newbie to Lustre so this overview is extremely light and hopefully what depth there is isn't full of mistakes!)

### Note on changes

The original document was

* based on Centos 6; this is for Centos 7
* assumed use of ZFS; this one uses Ext

### Note on instructions

The commands are presented in shell-script form, so that they can be easily copied and pasted into a terminal window.  *You should never blindly copy strings of commands into a terminal, especially as a privileged user.*  They are presented here because many of the commands must be replicated in multiple nodes.

## Instructions

**The following is needed for ZFS which is not required for this cluster, which uses the Ext filesystem as a basis for Lustre.**
<strike>
 * Downgrade kernel if needed (an upgrade may be required instead):
   * `yum remove kernel-$(uname -r)`
 * Enable EPEL repo:
   * `yum install epel-release`
 * Enable ZFS on Linux repo (**not sure why this is necessary**):
   * `yum localinstall --nogpgcheck http://archive.zfsonlinux.org/epel/zfs-release.el7_3.noarch.rpm`
</strike>

 * Enable lustre repos:
```bash
sudo sh -c 'cat >/etc/yum.repos.d/lustre.repo' <<EOF
[lustre-server]
name=CentOS-$releasever - Lustre
baseurl=https://downloads.hpdd.intel.com/public/lustre/latest-feature-release/el7/server/
gpgcheck=0

[e2fsprogs]
name=CentOS-$releasever - Ldiskfs
baseurl=https://downloads.hpdd.intel.com/public/e2fsprogs/latest/el7/
gpgcheck=0

[lustre-client]
name=CentOS-$releasever - Lustre
baseurl=https://downloads.hpdd.intel.com/public/lustre/latest-feature-release/el7/client/
gpgcheck=0
EOF

# upgrade e2fsprogs
sudo yum upgrade -y e2fsprogs

# install lustre-tests
sudo yum install -y lustre-tests

# create lnet module configuration (use appropriate interconnect in place of
# "tcp0" and appropriate interface in place of "eth0"
sudo sh -c 'cat > /etc/modprobe.d/lnet.conf' <<EOF
options lnet networks=tcp0(eth0)
EOF
```
* There is now a Lustre kernel installed; reboot to activate: `sudo reboot`
* On the MGS and OSS only, have the `lnet` module auto-load on boot:
```bash
sudo sh -c 'cat > /etc/sysconfig/modules/lnet.module' <<EOF
#!/bin/sh

if [ ! -c /dev/lnet ] ; then
    exec /sbin/modprobe lnet >/dev/null 2>&1
fi
EOF
sudo chmod 744 /etc/sysconfig/modules/lnet.module
```

 * On the MGS/MDT/MDS:
   * Intialise a disk or partition to use for lustre.
   * Create a lustre MDT:
     * `mkfs.lustre --fsname=whatevs --mgs --mdt --index=0 /dev/sdX`
   * Create a mount point and mount the lustre FS:
     * `mkdir /mnt/mdt && mount -t lustre /dev/sdX /mnt/mdt`
 * On the OST/OSS:
   * Intialise a disk or partition to use for lustre.
   * Create a lustre OST:
     * `mkfs.lustre --ost --fsname=whatevs --mgsnode=192.168.N.N@tcp0 --index=0 /dev/sdX`
     * Adjust the `--mgsnode` parameter for the address and protocol
        used for the MGS.
   * Create a mount point and mount the lustre FS:
     * `mkdir /ostoss_mount && mount -t lustre /dev/sdX /ostoss_mount`
 * On the client:
```bash
# load the Lustre kernel module
sudo modprobe lustre

# create script to load Lustre module on boot
sudo sh -c 'cat > /etc/sysconfig/modules/lustre.modules' <<EOF
#!/bin/sh

/sbin/lsmod | /bin/grep lustre 1>/dev/null 2>&1
if [ ! $? ] ; then
   /sbin/modprobe lustre >/dev/null 2>&1
fi
EOF
sudo chmod 744 /etc/sysconfig/modules/lustre.modules
```

  * Create a mount point: `mkdir /mnt/lustre`.
    * Mount the lustre FS:
      * `mount -t lustre 192.168.N.N@tcp0:/whatevs /mnt/lustre`