There is quite a bit to read recently about some new filesystems:

• Btrfs 0.16, Improved Scalability And Performance - Btrfs 0.16 was released on August 5, 2008. I haven’t tested Btrfs but I have noticed that the project has a lot more momentum than other filesystem projects. Hopefully they’ll stay on track for a 1.0 release before the end of 2008.
• Comparing HAMMER And Tux3 - A long and very technical discussion between the HAMMER and Tux3 filesystem creators. It’s well worth a read to understand what the latest and greatest ideas in filesystems are. Tux3 is another filesystem I’m paying attention to as long as there is test code released in the not too distant future.
• Tux3 Hierarchical Structure - More details on the Tux3 filesystem.

I decided to try ZFS-FUSE is my ongoing attempt to employ filesystem snapshots in my servers. ZFS-FUSE is in beta but I thought I would give it a try and see what happened. The install was not too difficult other than having to install a bunch of library dependencies along the way. These steps may work on other versions of Ubuntu, Debian, or other Debian derived distros but they have only been testing on Ubuntu 8.04.

I've concluded testing NILFS and found that even the latest version (2.0.5) is not ready for use. I was hoping to use NILFS to provide snapshots of virtual disks but I ran into nothing but trouble, I think due to the use of O_DIRECT by Xen which is not correctly supported by NILFS. My virtual machines with files on a NILFS filesystem complained of IO errors on their virtual disks. I like the design and tools of NILFS a lot so I will definitely keep an eye on it but it's not ready yet. Next on my list of new filesystems to try: ZFS-FUSE.

For a long time now I’ve suffered through a modem which disconnects any TCP session which has been idle for 15 minutes. For the most part this behavior is not problematic, except for SSH. I’ve gotten into the habit of trying to leave all of my remote SSH sessions running a program with continuous feedback such as top, htop, saidar, iftop, or watch. Of course there are plenty of times in the middle of work I don’t think to run a program and do some research only to come back to a dead SSH connection. I decided to finally address this issue and figure out how to send some sort of keep-alive. There are 2 options which can be used: ServerAliveInterval and TCPKeepAlive. Each of these can be used alone or together but there are benefits and drawbacks to each.

The available ciphers and cipher modes in the Linux kernel have evolved fairly rapidly over the past couple of years. Of course it is important to track the version of the kernel that particular crypto code gets merged so that backward compatibility concerns can be addressed. I decided to put together some information from 2.6.24 to try and decide what crypto options made sense for encrypted swap files and backup disks.

Update: Please do not follow the advice in this article. I had hoped that I had found a solution but in fact the steps outlined here, while preventing the problem of systems hanging at boot during a drive failure, introduce new problems. The best advice I can give right now is to wait for the fixes for Hardy to be released and hope for no drive failures on remotely administered systems. Yes, I know that doesn’t inspire confidence in Ubuntu on the server; nor should it. End Update

I’m not entirely sure why the default behavior with regard to RAID would be to fail on startup since the point of RAID is for a system to survive a drive failure. However, the default behavior for Ubuntu is for the system to fail if a RAID array is degraded at boot time. Not only will it fail to boot it will also fail to give any useful information and spend several minutes before delivering the user into a recovery console. A far more useful behavior would be to prompt for a number of seconds that an array is degraded and then continue to boot (with an option to reverse this behavior). In any case, this is not a difficult situation to remedy though finding the right information can be.

It would be nice to see Eclipse 3.4 and Neteans 6.1 included in Ubuntu 8.10. Requests have been filed and nominated for inclusion. The development community is certainly a group worthy of catering to.