Holy Cow – BTRFS!

Recently I have been experimenting with BTRFS. BTRFS is a relatively new filesystem which has modern features, high performance, scalability, supporting file-system snapshots and on-the-fly compression.

After spending the week running BTRFS on Ubuntu from within a Virtualbox VM I reinstalled my laptop using it. Ubuntu’s installer supports creating btrfs partitions, which is handy, and it is reported to work even as a boot partition. I had problems using BTRFS as the boot partition however, so elected to use ext2 for boot in the real install.

The installer doesn’t support enabling the on the fly compression, so once I had the system installed I edited /etc/fstab adding “compress=lzo”, I added “ssd” as I have an SSD and “space_cache” which is reported to improve performance. After I rebooted I ran a filesystem balance to compress any existing compressible data like so:-

btrfs fi balance /
btrfs fi balance /home

It’s worth pointing out here that there still isn’t a utility which can fix BTRFS filesystem corruption, so although BTRFS is considered stable, you may want to stay away from it just in case. There is also a nasty condition that can cause a kernel crash if the file-system runs out of space, so that is another one to watch for.

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Wake On LAN over wireless

What is it?

Wake On LAN is a mature technology for switching on computers over a network or remotely.

Why would I want it?

Perhaps you are a techy such as myself and you want to be able to switch customers computers on and work on them remotely (saves having to tell people to leave machines on if you are working after hours).

I also use it to switch on my Ubuntu machine upstairs when I am downstairs (saves me or my better half having to wait for boot or to get a file to or from the machine without physically going up there).

Is it easy to do?

Yes when you know how ;)

Before I go any further I will mention a caveat. Almost all of the WOL howto’s out there mention using a “magic packet” packet to wake the machine. Unfortunately I found out after much head banging and googling “magic packet” doesn’t work over wireless networks, apparently because wireless frames screw the magic packet up so that the wakee doesn’t recognise it any more.

So if you want to use WOL by sending the wake up through a wireless network your options are limited and it depends on the network card you have. At least 2 of the cards I have support a variety of WOL options “pumbg” and the other one only supports “pg”.

  • P stands for PHY activity
  • U stands for Unicast activity
  • M stands for Multicast activity
  • B stands for Broadcast activity
  • G stands for Magic Packet activity

Firstly I tried phy activity that had the unfortunate effect of starting the machine every few seconds. Then I graduated to broadcast which started the machine periodically (my thick wireless router is sending out broadcasts every hour or so). Eventually I settled on unicast here is how to get it working.

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