Basic ‘ZFS on Linux’ setup on CentOS 7

Here is a quick guide to getting a plain ZFS partition working on a Linux machine using the “ZFS on Linux” project.  I was playing around on a CentOS 7 virtual machine trying to set it up as a replication target for my home FreeNAS box as a backup.  If you are unfamiliar with ZFS, it is a filesystem for a storage environment, having features such as data integrity protection and snapshots; I came across it as it is used in FreeNAS.

Here is the procedure I used:

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“Error: Boot loader didn’t return any data” when booting up Xen guest

Error: Boot loader didn't return any data

I have come across this error two or three times before, and each time I spend hours trying to figure out how to get my virtual machine to boot.  This blog post is just to document a fix so that I can refer back to it, and hopefully it will help people out if they’re experiencing the issue as well.

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FreeNAS and ZFS

Since I built my home server back in 2012, I’ve had a FreeNAS virtual machine running on it as the file server of my home network.  For the past two years, I’ve been using it for the simplest of tasks (serving files).  But over the past week, I’ve started looking deeper at some of the cool things FreeNAS and ZFS can do.  The descriptions of each of these are going to be brief; they can probably be expanded to a full blog post, which I may do if I have time.  However, until then, if your interest has been piqued, you will have to do some additional research on your own.

FreeNAS web interface
One of the configuration screens on the FreeNAS web interface

First, let me briefly introduce what FreeNAS is.  FreeNAS is a system based on FreeBSD that primarily provides a network-attached storage (NAS) service for your network.  It uses the ZFS file system, which as you’ll see in a bit has quite a number of interesting features.  FreeNAS comes with a web interface where you can easily configure everything.

So with that introduction out of the way, let’s get into FreeNAS and ZFS!

CIFS, AFP, and NFS

In English, FreeNAS supports file sharing with Windows, Mac, and *nix computers. That was a pro for me because I have all flavours of operating systems on my computers at home.

The support for AFP (Apple Filing Protocol) includes Time Machine endpoints, which is something worth discussing in its own section below.

Networked Time Machine backups

It’s easy to setup Time Machine on your Mac using an external hard drive. However, unless you actually plug the drive in, there’s no backup opportunity.  For me, sometimes I use my computer in my living room, other times in my bedroom.  Sometimes my backup drive isn’t where I am working and I’m too lazy to go get it.  There must be a better solution.

If you’re willing to spend a couple hundred dollars for an AirPort Time Capsule, it will allow you to make backups over the network, even over Wi-Fi.  I actually bought one to try, but I returned it within a week because what it did really didn’t justify the cost.

Fortunately, FreeNAS has the option of enabling Time Machine endpoint functionality on AFP shares.  Now, whenever I’m at home within Wi-Fi range, my Mac will automatically make Time Machine backups.  Hands-free backups!  Awesome!  And with multiple Time Machine targets in OS X Mountain Lion, I’m able to have a backup to the NAS as well as a backup to an external drive whenever I get that plugged in.

Time Machine
My Time Machine configuration

One note is that networked backups are somewhat more finicky. The backup target gets corrupted more often than the one on the external drive.  However, I’ve noticed using OS X Mavericks and the latest FreeNAS builds that generally it is a lot more stable than when I first configured it.  Mostly, remembering to stop any current backups before turning off the computer will reduce the chance of corruption.

For more information about this, check out the following links:

Snapshots and replication

Now let’s talk about some of the features of ZFS, which FreeNAS nicely gives us access to through the web configuration.

At some point in time you may want to ensure that your data on the NAS is backed up at a remote location (because even the most complex RAID setups won’t save you in the case of a fire or flood).  This is where snapshots and replication comes into play.

ZFS snapshots are light weight and only store changed blocks.  This means that they are fast (don’t require downtime) and don’t take up much extra space on the disk.  Then, snapshots can be sent to another host with a ZFS volume over SSH.

FreeNAS’s web interface makes setting up automatic snapshots and replication very easy.  In addition, the replication target is quite flexible because all that is required is a host that has ZFS and SSH.  That means, it’s not necessary to be locked in to using a FreeNAS system as a replication target.  In fact, using packages from ZFS on Linux, most 64-bit Linux distributions can be used as replication targets.  I went with Debian as that was the easiest to setup for my particular case.

For more information about this, check out the following links:

FreeNAS plugins

I came across the plugins last week when I was diving a bit deeper into FreeNAS.  I haven’t explored this fully yet.

FreeNAS is primarily a file server.  However, as it’s a computer that’s almost always running, it makes sense to have other services run off of it so that a separate application server isn’t necessary.  This is where plugins come in.

The list of plugins is available on the FreeNAS wiki.  There is also an article on installing the plugins.

The plugins that I’m interested in are btsync (BitTorrent Sync), owncloud, and the media plugins.  Right now, I have a separate virtual machine that serves these applications while storing the data on the NAS.  Using plugins, this extra virtual machine may not be necessary!

Final comments

If you take a look at Wikipedia article on ZFS, there are a lot of interesting features in ZFS.  It supports its own type of software RAID to protect against drive failures.  It’s possible to encrypt and compress data sets as well.  This is just scratching the surface on what ZFS can do.

ZFS is a robust, reliable, and practical file system to be used as network-attached storage.  Combined with the web interface provided by FreeNAS, this functionality is able to be unleashed for usage in diverse environments.

Are you using FreeNAS or ZFS in an interesting configuration?  Have other tips for other users?  Post your ideas in the comments!

Saving keystrokes with a SSH client config file

I regularly have to SSH into my servers, and on most of the ones I connect to the SSH server is running on a non-standard port for obvious security reasons.  I used to include the port number manually in the SSH command, for example:

ssh seymour.dennistt.com -p 922

This worked… as long as I remembered to type the port number in, which was probably less than half the time on the first go.  So I finally got tired of having to retype the command with the port number in it.  Luckily you can create a SSH client configuration file which will remember this for you, and even give you a shortcut.
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XDMCP Login from Mac to Lubuntu 11.10

My old desktops run Lubuntu (Ubuntu but lightweight!) 11.10, which just became part of the official Ubuntu release.  Life is a lot zippier in Lubuntu compared to Ubuntu when you’re on Pentium III and Celeron machines.

I wanted to be able to login to these computers remotely with a GUI, sort of like Microsoft’s Remote Desktop but Linux style.  I didn’t want VNC because I wanted to be able to create a new login session instead of using the main console. Luckily XDMCP does exactly that and most of it is built into Ubuntu.

The Setup

Following one question previously posted on AskUbuntu, I proceeded to add the following snippet to /etc/lightdm/lightdm.conf:

[XDMCPServer]
enabled=true

Logging In

Then following the procedures posted by David Winter, I opened Terminal on my Mac, and typed in: /usr/X11R6/bin/X -query 192.168.0.1 (replace 192.168.0.1 with the IP address of your Lubuntu computer).  After a few moments the Ubuntu login screen showed up.  Perfect!

Terminal Shortcut

I made myself an alias so that I wouldn’t have to remember the complicated command line.  In ~/.bash_profile, I added:

alias xdmcp="/usr/X11R6/bin/X -query"

So now I can start a XDMCP session by typing in

xdmcp 192.168.0.1