ZFS NAS using CentOS 7 from tmpfs

Published Tuesday, October 24, 2017 (700 words, 4 minutes to read).

Following up on the CentOS 7 root filesystem on tmpfs post, here comes a guide on how to run a ZFS enabled CentOS 7 NAS server (with the operating system) from tmpfs.


  • HP ProLiant MicroServer
  • HP ProLiant MicroServer Remote Access Card
  • AMD Turion™ II Neo N54L Dual-Core Processor
  • 2x 8 GB 1333 MHZ ECC memory modules
  • 4x 4 TB SATA hard drives (HGST, Western Digital and Seagate)
  • Built-in Broadcom Limited NetXtreme BCM5723 Gigabit Ethernet adapter

Preparing the build environment

The disk image is built in macOS using Packer and VirtualBox. Virtualbox is installed using the appropriate platform package that is downloaded from their website, and Packer is installed using brew:

$ brew install packer

Building the disk image

Three files are needed in order to build the disk image; a Packer template file, an Anaconda kickstart file and a shell script that is used to configure the disk image after installation. The following files can be used as examples:

Create some directories:

$ mkdir ~work/centos-7-zfs/
$ mkdir ~work/centos-7-zfs/http/
$ mkdir ~work/centos-7-zfs/scripts/

Copy the files to these directories:

$ cp template.json ~work/centos-7-zfs/
$ cp ks.cfg ~work/centos-7-zfs/http/
$ cp provision.sh ~work/centos-7-zfs/scripts/

Modify each of the files to fit your environment.

Start the build process using Packer:

$ cd ~work/centos-7-zfs/
$ packer build template.json

This will download the CentOS 7 ISO file, start an HTTP server to serve the kickstart file and start a virtual machine using Virtualbox:

Packer installer screenshot

The virtual machine will boot into Anaconda and run through the installation process as specified in the kickstart file:

Anaconda installer screenshot

When the installation process is complete, the disk image will be available in the output-virtualbox-iso folder with the vmdk extension.

Packer done screenshot

The disk image is now ready to be put in initramfs.

Putting the disk image in initramfs

This section is quite similar to the previous blog post CentOS 7 root filesystem on tmpfs but with minor differences. For simplicity reasons it is executed on a host running CentOS 7.

Create the build directories:

$ mkdir /work
$ mkdir /work/newroot
$ mkdir /work/result

Export the files from the disk image to one of the directories we created earlier:

$ export LIBGUESTFS_BACKEND=direct
$ guestfish --ro -a packer-virtualbox-iso-1508790384-disk001.vmdk -i copy-out / /work/newroot/

Modify /etc/fstab:

$ cat > /work/newroot/etc/fstab << EOF
tmpfs       /         tmpfs    defaults,noatime 0 0
none        /dev      devtmpfs defaults         0 0
devpts      /dev/pts  devpts   gid=5,mode=620   0 0
tmpfs       /dev/shm  tmpfs    defaults         0 0
proc        /proc     proc     defaults         0 0
sysfs       /sys      sysfs    defaults         0 0

Disable selinux:

echo "SELINUX=disabled" > /work/newroot/etc/selinux/config

Disable clearing the screen on login failure to make it possible to read any error messages:

mkdir /work/newroot/etc/systemd/system/getty@.service.d
cat > /work/newroot/etc/systemd/system/getty@.service.d/noclear.conf << EOF

Now jump to the Initramfs and Result sections in the CentOS 7 root filesystem on tmpfs and follow those steps until the end when the result is a vmlinuz and initramfs file.

ZFS configuration

The first time the NAS server boots on the disk image, the ZFS storage pool and volumes will have to be configured. Refer to the ZFS documentation for information on how to do this, and use the following command only as guidelines.

Create the storage pool:

$ sudo zpool create data mirror sda sdb mirror sdc sdd

Create the volumes:

$ sudo zfs create data/documents
$ sudo zfs create data/games
$ sudo zfs create data/movies
$ sudo zfs create data/music
$ sudo zfs create data/pictures
$ sudo zfs create data/upload

Share some volumes using NFS:

zfs set sharenfs=on data/documents
zfs set sharenfs=on data/games
zfs set sharenfs=on data/music
zfs set sharenfs=on data/pictures

Print the storage pool status:

$ sudo zpool status
  pool: data
 state: ONLINE
  scan: scrub repaired 0B in 20h22m with 0 errors on Sun Oct  1 21:04:14 2017

	data        ONLINE       0     0     0
	  mirror-0  ONLINE       0     0     0
	    sdd     ONLINE       0     0     0
	    sdc     ONLINE       0     0     0
	  mirror-1  ONLINE       0     0     0
	    sda     ONLINE       0     0     0
	    sdb     ONLINE       0     0     0

errors: No known data errors