Building a better NAS for use with Macs, part 2 - The current environment

Building a better NAS for use with Macs, part 2 - The current environment

The current setup (snapshot january 2009) consists of:

1 machine running OS X Server (MacBook Pro)

• booting off an external 500Gb USB drive

• three disks in a concatenated RAID for holding Time Machine backups (2x750Gb, 1x500Gb)

1 media server, connected to the TV in the living room (Intel Mac Mini)

• booting off an external 500Gb firewire disk

• iTunes library, including films stored on an external 1Tb firewire disk (mostly my region 1 DVD collection bought before moving to France)

1 MacBook Pro for daily use

• internal 250Gb drive

• various external portable drives

• 1 USB 250Gb drive for SuperDuper! backups (variable schedule)

The two fixed machines are linked via two Airport Extreme Base Stations, connecting over the 5Ghz channel. Both machines are connected to the base stations via ethernet.

On the office Airport Extreme, there is a 1Tb USB drive connected which is used to hold a disk image of the media drive, copied via SuperDuper. Not an ideal solution, but I didn’t want to push all of that data into Time Machine and extend the existing volume since one failure on any of the disks in the concatenated RAID set renders the entire thing useless (something that keeps me up at night). So a one to one backup seemed the most appropriate solution. If the main media disk dies, I can swap out the backup, mount the disk image and be back in business quickly.

The Time Machine volumes on the server hold the backups for all machines (media drive excluded). Time Machine to a network share is a viable solution but it does present some issues over a slow wifi network, notably that you incur the additional overhead of managing the disk images. A disconnection will result in hdiutil having to rescan the entire volume at the next backup and this can take hours. So it works, but there are times I find myself swearing at it if I leave the house quickly and forget to check if there’s a backup in progress. For that reason I sometimes connect directly to an ethernet connection in the office.

My MacBook Pro and the Media Mini are using OS X Server’s Portable Home Directories to keep a local copy of the home directory that is synchronized with a copy on the server so I have a quick means of recovering an account on any machine should the need arise. It’s a little flaky from time to time, but since 10.5.6 I’ve noticed a net improvement in the reliability. That’s also part of the reason that the iTunes library is on a separate disk - I didn’t want the PHD making a copy of everything since there’s not enough disk space on the server and PHD syncing had been causing me some grief pre-10.5.6.

Additional (irrelevant) bits and pieces:

• 3 Airport Express base stations, used for managing the 802.11g network accessed by my wife’s PC and our iPhones as well as distributing music around the house from the Media Mini.

So things look like this:

Unfortunately, the layout and age of the house currently preclude easily running physical ethernet cables between the base stations, but I’m working on a solution since that would enable a few other possibilities like the ability to move the user home directories to the OpenSolaris server and get rid of local disks entirely on the Media Mini. The AEBS in the living room is the older 100Mb ethernet version that will have to be replaced if I manage to figure out how to run the cables discreetly (if it’s ugly it won’t get through the spousal approval process).*

It’s worth noting just how big a jump there is between 100Mbps and 1000Mbps ethernet. It’s obvious that it’s 10 times faster, but most people don’t stop to evaluate exactly what that means in real life. With 100Mbps ethernet, I can saturate the connection from a portable 5400RPM USB drive since the network transfer rate maxes out around 8MB/s. Now in a lot of cases, this isn’t a big deal, but it means that there’s not a lot of headroom for competing access. This means that streaming an HD video at the same time as a Time Machine backup is running is likely to cause problems for both. At gigabit speeds, transfer rates max out around 88MB/s which takes several disks to saturate a link. The net result is that I can be copying my entire media library to the NAS from the current disk at about 30-35MB/s (capped by the speed of the source disk) and still have a ton of bandwidth left over for everything else going on.

On the Wifi front, the theoretical top end of 802.11n is 300Mbs which is definitely a step in the right direction, but that’s under ideal conditions and there’s a heck of a lot more latency in the connection that there is over a wired one. Currently the connection speed between the two bases stations fluctuates between 45Mbps and 120Mbps. In practical terms this means that the initial backup of 700+Gb of data across this link is a multi-day process.

If you’re wondering just how fast your Airport connection really is, check out the neat, almost hidden feature in the Airport Utility to watch connection speeds from various clients.

Open the Airport Utility

Double click a base station from the list and wait for the screen to load completely

Click on the title for Clients

Next up: Getting started…

Previous: Introduction

* This was drafted before the new Airport Base Stations were released and it looks like the new multi-band option is exactly what I’ve been looking for.