thirdbIT

LVM2 is a very useful thingy indeed. I sort of misunderstood its utility for a while. It’s not just for managing storage on mongo SAN clusters; it can be very useful for managing storage on a workgroup box with several drives.

However, on Linux, beware: You cannot boot from an LVM logical volume. You need to have a regular filesystem (ext2/ext3/xfs/jfs/reiserfs/etc.) partition for /boot. I’m not quite sure why I didn’t grasp this when planning my first LVM layout.

The Red Hat documentation on LVM2 is excellent, but is not the first thing that comes up on searches, because it’s buried in the weirdo RHEL system documentation. There’s a similar, RedHat-generated doc which is also good at the CentOS project, available here.

It takes some getting used to to understand LVM, and if you’re like me, it doesn’t hurt to practice. There is some degree of overlap with what RAID can do for you, and using them both together makes one’s head spin at first. Drawing a map of your planned layout is extremely helpful.

For wrangling your storage layouts, the Parted Magic live CD can be very helpful. Unfortunately, not all installers want to respect what you’ve laid out with it. Fedora 9 played nice. Ubuntu 8.10 (alternate install CD — essential for RAID installs) was not; it kept not respecting the /dev/md software RAID devices that I’d previously set up, then would create some new bogus md devices.

VMware Fusion is a wonderful thing. I am happily running three Linux instances at once under my MacBook with 4GB of RAM (though, as best I can tell, the mobo can actually only address 3GB of RAM).

One glitch that was driving me crazy, though, was that it seemed like DHCP leases were being allocated flakily to the guest machines. When you’re doing database replication, you can’t have master/slave IP addresses changing all the time. (And you certainly don’t want two machines with the same IP address!)

Some digging around turned this up. I don’t remember exactly where — I believe snippets of it were in an official VMware forum — but it was harder to find than it should have been. Hence my posting, to add another path to help those who need it.

On OS X, the file you need to change should be in /Library/Application Support/VMware Fusion/vmnet8/dhcpd.conf. (vmnet8 is the virtual interface for NAT networking in the guest machines.) You should have a subnet clause in it already like this:

subnet 172.16.253.0 netmask 255.255.255.0 {
    range 172.16.253.129 172.16.253.254;
    option broadcast-address 172.16.253.255;
    option domain-name-servers 172.16.253.2;
    option domain-name "localdomain";
    option routers 172.16.253.2;
}

Now, for each virtual machine, set up a new host clause, e.g. :

host ubuntu64-vm {
    hardware ethernet 00:0F:FF:EF:00:00;
    fixed-address 172.16.253.20;
}

Be sure to assign an IP address (fixed-address) outside the range specified in the subnet clause at top.

Get the Ethernet MAC address from ifconfig eth0 inside the guest machine, or from ~/Documents/Virtual Machines/GUESTMACHINENAME/GUESTMACHINENAME.vmx (it’s the line with ethernet0.generatedAddress).

Finally, restart the requisite VMware daemons by running

sudo "/Library/Application Support/VMware Fusion/boot.sh" --restart

I bought the elegant little Apple Airport Extreme back in the summer. Network disk (pseudo-NAS) support! Printer sharing! Fantastic! Besides the fact that our last wireless router was puking to death again (why does that always happen to us after <2 years? Do I emit gamma rays from my head?), I was excited to enable USB printer networking and shared network drives.

Only in both cases, they don't work. At least not in a way that is useful to me.

1) Printer sharing

There are two defects here: one design, one implementation. After trying to figure out why I couldn't do anything that my fancy-ass new multifunction printer that Canon sells as a loss leader for its pricey ink cartridges, I discovered that it it normal that non-printing functions don’t work unless the unit is directly connected to the computer. Networks are for printing only. No scanning, no ink maintenance fancy stuff, just printing. That’s the design problem, and it’s a major bummer, but it wasn’t a deal killer. (OK, well, nothing was a deal killer; I bought the damn thing.)

Nope, what ended network printer sharing for me was that the shared network printer would periodically disappear or otherwise become unavailable for users on the network. Had to delete the printer and re-add it, or at the very least power down the router and printer and power up again. That’s crap. So now the way I provide reliable-ish network sharing is to connect it directly to my computer and share it as a network printer.

That’s crap.

Grade: F. I would blame Canon, because they make great hardware and execrable software, but I had a similar problem with my old HP Laserjet 6MP printer.

2) Drive sharing

I finally got my ass in gear and moved my old 250GB USB drive from my slowly-decommissioning Windows machine onto the Airport Extreme. After many slow reboots of the router (yeah, any change requires a reboot; couldn’t it at least boot faster, damnit?! I’m not even getting a DHCP lease from my ISP — it’s static.), I discover that the Airport Extreme is unable to share NTFS volumes. Well, that’s not so multi-platform, now, is it? FAT32 is insecure and doesn’t work for big volumes, say, any hard drive created after about 1998. HFS+ would have been an option if this drive were originally on a Mac, but it wasn’t. So my best options are:

• Copy all of the data off the drive and reformat to HFS+; remount on the Airport Extreme after getting their wonky SMB networking
• Abandon the project, as the USB drive is already 5 years old and isn’t worth spending a lot of time monkeying with

Guess which one I picked?

Grade: D+. You’ll note that the spec sheet mentions nothing about not supporting NTFS. I’d like to blame M$ for that one, but there are plenty of NAS vendors that offer NTFS support.

While I’m at it, let me complain about Apple file sharing. You seem to be able to choose between a yucky slow SMB implementation and AFP (which does appear to be much faster, at least for authenticating). I have grown frustrated with both and am now very, very happily using instead sshfs, which is great both on the LAN and across the Internet. Too bad ‘Doze doesn’t support user-space filesystems; so no sshfs for Windows.

(To run SSHFS, I use Google’s MacFUSE project and their SSHFS executable. I don’t remember exactly why, but the MacFusion GUI doesn’t work on my machine.)

Ubuntu seems to be the big distro these days. (Remember all of those other “it” distros? Slackware? The original Red Hat? Mandrake? I am vaguely tired of the trendiness of distros.)

Anyway, there is no package yet for Ruby 1.8.6 on Ubuntu Feisty Fawn (7.04), which is unfortunate, since mongrel_cluster doesn’t work properly under Ruby 1.8.5.

The install steps I got at Urban Puddle (here) were nice, but Rails still wasn’t happy: I kept getting that awful `require’: no such file to load – rubygems (LoadError) error.

Here’s what I did to fix it. YMMV.

Building Ruby (from Urban Puddle):

tar xjvf ruby-1.8.6.tar.bz2
cd ruby-1.8.6
apt-get build-dep ruby1.8
./configure --prefix=/usr
make
sudo make install

Next, to fix it:

cd /usr/src/rubygems/rubygems-0.9.4
sudo ruby setup.rb

Et voilà :

max@somehost:~ $ irb
irb(main):001:0> require 'rubygems'
=> true

I’m not quite sure why the Ruby source doesn’t ship with the rubygems source. Is it because rubygems is still a < 1.0 release?

I just blew a frightening amount of time (mostly unbilled) tracking down the most aggravating problem I’ve seen in a while.

The way that the “production” version of Trac (which is at 0.10) works with Unicode is a bit dim. Somewhere laced in there it likes to use the default encoding of latin-1 instead of utf-8. (It’s not in the standard siteconfig.py location, though.)

The errors I was getting when trying to sync Trac to the SVN repository were like this:

2007-09-16 22:51:59,995 Trac[cache] WARNING: Revision 11 already cached: 'latin-1' codec can't encode character u'\ufffd' in position 43: ordinal not in range(256)

I tried a number of approaches, including rebuilding swig, subversion, python, and some others. None solved the damn problem, though I obviously encountered new ones along the way. Amy managed to refocus me properly on the goal by verifying that the problem was indeed caused by Unicode characters in filenames the Subversion repository, and by picking at the Trac code that inserts SVN data into its database. In attacking that problem I converted the Trac database to the utf-8 character set from latin-1, which would have been a problem. That still didn’t fix it, though.

It wasn’t until I tried resyncing using trac 0.11dev’s trac-admin tool that it finally worked.

Trac’s site does warn that 0.10 still has some problems with Unicode. There’s even a ticket pointing out a fix which I really didn’t want to apply myself, knowing it would get rebroken at some point. (One commenter noted that “this should be backported to the 0.10 line”, but unfortunately that doesn’t seem to have happened.)

Update: I’m fairly confident that, had I started with a utf8 MySQL database to begin with instead of latin1, I would have avoided all of these woes. But that wasn’t my starting point. (Fun fact: Python calls them “latin-1″ and “utf-8″, while MySQL calls them “latin1″ and “utf8″. Strangely enuf, that difference didn’t cause me any problems.)