Last week I had a hard disk crash. If you’ve had a hard disk crash you may know it can take a day or two to get things up and running again, a day or two that I didn’t have. I was flat our trying to get away on holidays before Christmas. Thankfully, I have a Promise Pegasus RAID array, and I can’t believe how great it was. I was up and running again in 30 seconds – I kid you not! This article describes how it works for those who might be interested.
Back in August 2011 I purchased a Pegasus Promise 4 bay external RAID array. It set me back almost $1000. It seemed like a lot to spend on a hard drive enclosure. But I had just downgraded from a Mac Pro to a Mac Mini, and at the same time I switched across to a Pegasus RAID for my storage. I figured that the speed improvement of running 4 drives as a RAID might make up for the Mac Pro. And to some extent it did.
RAID is the technical term where you have a number of hard disks running in parallel, and the computer sees them as one. This can, depending on how it is set up, give you a huge speed boost as well as better reliability. On one extreme, you could run the 4 drives to store 4 times the data and 4 times the read speed (because the controller spreads one file out over the 4 drives, and then reads from the 4 drives in parallel, so that the data is coming in 4 times faster! On the other hand you could duplicate the same information of all 4 drives, like having 3 backups. RAID is more complex than this, but that’s the rough principle.
Out of the box the Pegasus RAID runs as what is called RAID 5. (This describes RAID 5.) This means it takes the 4x 1GB drives and makes them into 1 drive of 3GB. There is a spare GB in there. This lost GB is spread across the drives so that if any one of the drives fails, no data is lost.
The Pegasus unit takes 4 drives. I put 4x 1TB drives in my Pegasus unit. There is 4GB worth of hard drives, but the computer only sees 3GB of disk space. This 3GB is spread across the hard disks in such a way that if any one hard disk fails, the other 3 hard disks contain all 3GB of my computers data.
So if hard disk 1 fails, disks 2,3&4 have all my data. If disk 2 fails, Disks 1,3&4 have all my data. If disk 3 fails, disks 1,2&4 have all my data. And if disk 4 fails, disks 1,2&3 have all my data. This is clever, the RAID controller takes care of it all automatically.
What it looks like in practice.
In practice you turn on the drive, and it works like any other hard drive. You wouldn’t know it was there, except that it’s a bit faster.
But, here i am 4 years later writing about it, because when one of my drives actually failed, it was amazing to have the RAID kick in.
Last week, my computer froze, and my pegasus unit started beeping, and one light went red to show that the top drive had failed.
All I had to do was eject the top drive, and restart my computer and it automatically started running from the bottom 3 drives alone. All my files were there, even the one I was working on when it crashed. My computer was perfectly normal! You would not have known anything happened. (Except that there was a beeping from my Pegasus unit to let me know there was a problem – one of the drives was missing!)
Of course, I was now running off 3 drives so if one of those went down I was in trouble. So the first thing I did was a backup of my computer.
To get my RAID system up and running again I had to go and buy a new 1TB hard disk from Officeworks, put it in the top slot, and ‘rebuild’ it. This was mostly automatic, but I did have to tell the unit to start the process. I had to open my Promise Utility, click ‘Physical Drive Settings’ and click the radio button that said ‘unconfigured.’ Then I had to go to Disk Array and select ‘Rebuild’.
The Pegasus unit then took about 2-3 hours to rebuild my 4th drive from the existing 3 drives. It copied all the data it needed from the other 3 drives. While all this was happening I could still use my computer. The rebuild happened in the background – I could still open and save files!
When it finished, I had all my drives working again with blue lights.
Out of all the backup and hard drive solutions I have come across this is by far the best.
Now the Pegasus unit costs a lot, in Australia it’s over $2299 from the Apple Store.
On Amazon they go for around $1300.
I purchased my Pegasus unit from Other World Computing, but I just checked and they no longer sell them. They do sell their own external drive array for $399. I have never tried one of these, but it might be a good solution if you can’t afford a Pegasus.