The RAID 5 Sublimation

It's one thing to research and order the right parts for an external RAID array, but it's another thing to assemble, configure and activate it. In order to make this technology work, you need the following abilities:

  • You must be able to read at or above the 4th Grade level
  • You must have opposable thumbs
  • You must be able to use a Philips-head screwdriver
  • You must possess either great physical strength or a pair of scissors (the latter is recommended)
  • You must be able to flip tiny switches, perhaps with a flat-head screwdriver (note: there is one exception to this requirement)
  • You must be able to plug in cables that will only fit if aligned correctly.

If you can do these things, then you can install a RAID array.  It's amazing how often technology is really less complex than the alternative. For example, take something as natural as fire.  Would you rather create fire by the friction of rubbing two sticks together, or would you prefer to flick your Bic? Technology is your friend.  It assumes that you're stupid, which is why we love it.

Some Assembly Required

As you may recall if you read yesterday's post, I ordered four hard drives and a RAID enclosure. In order to make this function, I need to put the various pieces together. The manual is a thin pamphlet. Although it may be 40 pages long, there isn't much text and there are plenty of pictures. People like pictures. Read the manual and you realize that most of it is obvious.

The next thing you need to do is open the enclosure. This is where opposable thumbs are quite handy (no pun intended). You place the enclosure on your desk, put your hands on both sides, and slide the top off with your thumbs. If this doesn't work for you, there are two techniques you can use to trouble-shoot the problem:

  • Be sure that the top is actually on top where you're placing your thumbs.
  • If it won't slide in the direction you're pushing, turn it around and push the other direction.

Once you open the enclosure, you'll see it's empty, with the exception of four rails.  You must attach these rails to each of the four hard drives. This is where the Philips-head screwdriver comes in handy.

OPTIONAL:  The package includes a set of stickers numbering from 1 – 4. You can place these on the rails so you know which one is which. Why does it matter?  Suppose you take the drives out and need to re-insert them in the right slot. How will you know if you don't have some form of identification? After all, they tend to look alike. I'm not sure why they couldn't just come with numbers already on the rails, but I presume it has something to do with lowering their production costs. Once again, opposable thumbs are desirable for this task.

Each hard drive has two screw-holes on each side. The enclosure comes with enough four screws for each drive, so don't drop them. All you have to do is put the screws through the holes in the rail on each side of the drive. When complete, it should look like this:

As you can see, the rail forms a nifty little handle. Use it to lift the drive and insert it into the bay. Then give it a little bit of a nudge to connect it in the back. Fortunately, there is only one way you can screw this up. The enclosure has openings for the rails and the screw-holes on the drive are offset to the correct side. You can only insert the drive correctly, as it will not fit if you have the drive upside down. The only error you can make is by putting the rail on upside-down so the number appears in the wrong direction when you look at the bay. It doesn't affect operation of the unit, but it makes you feel stupid if you do it wrong. Repeat this process until you have all four drives inserted in the enclosure (hopefully with all the numbers in the right direction) and replace the top of the enclosure.

The next step is to configure the dip-switches to determine the type of RAID configuration you want, and identity the number of of disks allocated to the unit. This is optional if you accept the default setting, which as it happens, is RAID 5 with 4 disks (yay me!). I recommend using a small, flat-head screwdriver for this task, unless you have really spindly fingers.

Next, connect the preferred data cable to your computer (USB, FireWire, eSATA). Each of these only fits in one direction, so it's hard to screw up. Finally, attach the power cable and turn on the power button.

Congratulations! You've just assembled and configured your RAID array. Don't get cocky yet, though. There's more work before you can use it.  The drives need to be formatted before they can hold data.

If you use a Mac, just bring up the Disk Utility and choose the Mac OS Extended (Journaled) option.  Sure, there are other options, but those choices suck. Partition the drive and now you have 6 terabytes of awesomeness at your disposal (assuming you ordered the same 2 TB drives that I did).

If you use a Windows system, I recommend you dump it and get a Mac. That's what I did, so it would be disingenuous of me to recommend another course of action. I suppose you could partition it and format the drive with NTFS or FAT32, but then it won't be awesome.

Now What?

OK, you have 6 terabytes of awesomeness. How are you going to make use of it? My primary concern was to offload my images from the internal 1 TB drive to the external drive. I had a few options to consider.

Since I use Aperture 3, and I use Managed photos in a Library, all I really had to do was drag the Library and move it from one drive to another. Actually, I have four libraries to manage the size. They range in size from 125GB to 180GB. Moving them to the RAID would give me plenty of room for growth, but there were other benefits at hand.

Hard drives perform best when they are less than 50% full. By freeing up room on my internal drive, I'm increasing its ability to perform. By separating my data from my applications, I gain further benefits by having multiple drive spindles reading files to open instead of requiring a single drive to do all of that work. Finally, having my Libraries on the RAID system gives me a bit of extra protection from drive failure. Yes, I keep backups, but those are only as good as the last point in time when I performed a backup. Now I have another recovery option just in case my backup isn't as up to date as my latest changes.

However, there are other concerns. The Mac OS uses a Home directory that's pretty convenient, and it includes a Picture folder that contains my Aperture 3 Libraries. If I just move the Libraries, I'm abandoning that convenience. Could I move the whole Pictures folder? If I could do that, maybe I could move the entire Home folder and give the same protection to my iTunes library and other documents. That would be nice and would free up even more space on my internal drive.

Relocating Home

It turns out that Snow Leopard makes it pretty easy to move your Home from one drive to another. In theory, all you need to do is copy the files over, go to the Accounts page in your Preferences and tell it where to find the new Home. Restart the system and now your home is on the RAID array.

In practice, there are potential problems. If you move the files using the GUI, you may not also move the user permissions with the files. When you try to login again, you discover that you can't do it because the system can't find your Home. If you don't have another administrator account, you're screwed.

To get around this potential problem. you need to open the Terminal shell and type a command to move the files, rather than use Drag & Drop. The command is “ditto” and it looks like this:

sudo ditto –rsrc “Users/William” “Volumes/RAID 1/Home/William”

The “sudo” command instructs the system to use Administrator rights to make this command work correctly. Essentially, you're telling the system to run the command as another user, and you'll be prompted to enter the password for administrator rights.

“Users/William” is the path to my Home directory. You need to replace that part with your source directory, which is likely in the “Users/” directory, followed by the short-name for your account. The next part describes where to move it. “Volumes” refers to a different drive. “RAID 1” is the name of my volume, or drive. “Home/William” is the directory structure I made on “RAID 1”.

The key to making this work is the “–rsrc” attributes that tell the “ditto” command to move permissions along with the files:

 --rsrc Preserve resource forks and HFS meta-data. ditto will store this data in Carbon-compati- ble ._ AppleDouble files on filesystems that do not natively support resource forks. As of Mac OS X 10.4, --rsrc is default behavior.

It's going to take some time to move the files. In my case, I had 789 GB in my home directory. This would be a good time to visit your favorite restaurant for a tasty treat, or do as I did and go to bed. Once the files complete copying, you don't want to make any other changes to them before performing the final step.

You need to have Administrator rights to change the Home directory, so expect to be challenged for another password.

Open the System Preferences and select the Accounts icon. From that window, click the Lock icon in the lower left corner to gain access to change user accounts. This should prompt you for an account with Administrator rights. Once you unlock the accounts, select the User Account that owns the Home folder you want to move. Right-click (or Control-Click) to access a context-menu that says “Advanced Options…” This opens another dialog box with ominous warnings:

Account Options...

The only line that matters to you is the Home directory and the Choose… button beside it. As you can see, this is the path to my new RAID array. All you have to do is click the Choose button and navigate to the copy of your home directory on the RAID system. Once you select it, the system will prompt you to restart. After the restart, your Home directory now resides on the path you selected.

I verified files, the number of files, the size of the files. Everything was moved over properly. I also had up to date backups of all my important data. After testing to see that Aperture 3 loaded from the correct Libraries in the new Home folder, played music in iTunes from the new source, all I had to do was delete the original files on my internal drive. At one time, I had less than 80 GB free on that internal 1 TB drive. Now I have 915 GB free. That sucker spins up nicely now without having to chug through a lot of directory info!

Internal Drive


I'm pleasantly surprised to find that the FireWire 800 speed is better than I expected. I'm not sitting here waiting forever for files to open or write back. Having my applications on the internal drive and data on the external drive does a nice job of splitting the load and seems to make Aperture and Photoshop a little faster. When I ultimately upgrade to a new iMac and have an eSATA port installed by OWC, I should see even more improvement.

Hell, I'm a happy puppy now. It's a sublime feeling. I have better performance. I have room to grow for bucketloads of photos I even have a row of blinking lights so I can tell when something is hitting my drives. That satisfies my geek soul. Adding a RAID array is a simple thing that anyone can do by following some rather simple steps.

Some Precautions

There are some things to always keep in mind. RAID can enhance your data protection, but it's not a substitute for backups. If my enclosure develops a problem, I've lost access to my data until I get it fixed or replaced. RAID 5 can tolerate one disk failure, but two disk failures would cause me to lose my data. Even if you don't lose any data on your RAID, there are other mistakes (e.g., user error) that may cause you to want to restore from an earlier version. You can't do that if you just over-wrote your only copy of a file. Backups are essential.

Also, you're now tethered to this RAID enclosure. If you pull out the plug, you can't even login with that account. Make sure you have another Administrator account handy in case your primary user account fails, and keep the Home director for that Administrator on your internal drive.

Your internal drive is not invulnerable. Like all drives, it will fail one day. That isn't something you can just restore from a backup. You'll have to install a new drive and load up the OS and your applications just like it was a new system. However, once you've done that, you can point it to all of your data safely tucked away on the RAID enclosure.

Happy motoring.

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