Xserve Notes

Software RAID Partitioning Best Practices

All recent Macs support software RAID in the BIOS, including the Xserve. However, it can be difficult to set up, and there is very little advice on best practices for how best to use it.

The key issue is that unlike many other operating systems that support software-based RAID, you can only RAID entire drives, not individual partitions.

Thus on the Xserve G5, there appear to be two choices:

• Build a mirrored RAID 1 out of the first two drives, install the OS on it, and use the third drive as a backup drive that is easily removable, or as a hot spare. This solution appears to offer the most reliable boot, as if the first drive fails, the second drive is still bootable. However, the system files and data share the same partition, making backup and restore more difficult.
• Install the OS on a non-RAID drive, and use the second and third drives for data using mirrored RAID 1. The advantage of this is that you can partition the first drive into several smaller volumes, making it easier to restore the system. The disadvantage is that if the boot drive fails, you can't boot until you recreate it. Another disadvantage is that the Mac OS X Server 10.4 installer doesn't easily allow you to separate system files from data.

I've tried both approaches, but I'm now leaning toward second. My first drive has 4 partitions -- 3 identical 30GB partitions, the remainder a spare volume. The first 30GB partition I boot from and is my working OS. The second partition is a clone of the first, in which I use Carbon Copy Cloner on a regular basis to keep up with the boot drive. The third is for experimenting, but for now I keep a copy of the OS X Server in stand-alone mode before I made any changes or added any services.

One particular advantage of this scheme is that I can use Carbon Copy Cloner to update the clone on the second partition, and then use Disk Utility to image it without rebooting the system (you can't image a boot volume with Disk Utility). This image I then store on an old iPod. This means that if anything goes wrong, I can quickly restore the disk image into a replacement boot drive without touching the RAIDed data drive.

There is also an option in Carbon Copy Cloner to support the creation of something called ASR  (Apple Software Restore) disk image which can be burned onto a DVD-RW which sounds like it would make reinstalling even easier.

The challenge of using this scheme is separating out the data from the boot volume, which I will leave for future blog posts.

Headless Video Support

Inspite of my problems installing OS X on a the Village Tronic MPDD Pro video card, the card does offer one feature that I like: optional headless support.

You might wonder why this might be important feature to have on a video card for a server? I've run into this problem before -- you attach a large monitor to a server and set the resolution high. You then put the server in the rack, and maybe a year later you need to put a monitor on it. However, this time, the monitor is the one in your machine room and it doesn't support the high resolution of the first monitor, so you can't get your monitor to work. This can be a real pain to solve.

What this optional patch does detect if there is no monitor attached and then lower the resolution to broadly supported size. The next time you attach a monitor, it will use this lower size.

Installing OS X 10.4 Panther with a Village Tronic MPDD Pro Video Card

I just purchased two used Macintosh Xserve G5s, however, they were configured very unusually. Rather then an Apple-branded video adapter they had a third party video adapter, the Village Tronic MPDD Pro.

The first Xserve doesn't have a RAID card, so attempted to install it first. When I tried installing OS X 10.4 Panther Server from DVD-ROM, it would start up OK, however, as soon as the bios was complete and the OS was started, the screen would go blank. My best guess is that there are no drivers for this card by default in the OS X installer DVD.

My first attempt was to boot the Xserve with FireWire Target Disk mode, and install using my Powerbook. I was able to use Disk Utility to mirrored software RAID drives 1 & 2, however, the installer would not let me install the RAID volume in FireWire Target Disk mode. So I installed the server on the spare drive 3. This worked up to very basic level, but even once installed, once OS X started, the video display would still die. Thus the drivers for this video card are not only not on the installer, they are not included with the system. So I couldn't finish the installation without a display.

As you can do a fresh install of OS X on headless Xserve with no video card at all, my next attempt was to use that technique. I got that working after a lot of pain searching for the correct serial number, which is used as the default password. This time I was able to install OS X on the mirrored software RAID volume. However, once you install, how do you install a video driver? I've never figured out how to remotely turn on Apple Remote Desktop and to configure it to turn on the "VNC viewers may control screen with password" option. So without the GUI, how do I install that driver?

So next I booted my Powerbook on the freshly installed OS X Server using FireWire Target Disk mode. This gave me the GUI, and was able to install the video drivers. I had to reboot twice to get them to work, but now my video card was working and I could use my regular monitor and keyboard.

I am mystified how the company that I bought the used Xserves from installed their OS X Server. It was clear to me from their setup of their machines that they had little experience with OS X Server, and I doubt that they installed using my technique. So either it came from CDW with the video driver already installed, or they figured out some other technique.

Now that I've got the first Xserve running, next I've got to try the same technique on the next Xserve, which has a hardware RAID card. Apparently the installer doesn't understand the RAID card, so you have to ssh into the installer and use the CLI (command-line interface) to configure the RAID. I'm not looking forward to it.