Saturday February 11, 2012 10:08 AM AEST

Atomic MPC > Opinions > David Field > RAID 5 = Relinquish All Indispensable Data 5

David Field

RAID 5 = Relinquish All Indispensable Data 5

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By David Field
15:55 Mar 11, 2008

Backups are for the weak! I have redundancy and a hardware card! Oh crap!

There are many horrible, sinking feelings that any proper PC user is all too familiar with. Yet no matter how acutely aware of the potential problems you are, you can never prepare yourself for their aftermath when they occur.

The smell of expensive burning silicon. The sight of an expensive scratched monitor. The utter, irreconcilable grief and emotional trauma of a failed RAID and the subsequent loss of 1.36-odd terabytes of work, video footage, projects, photos and oh-so-very-much more.

No prizes for guessing which of the three’s just happened to me.

Yep. And the worst thing was how unlikely I thought the failure would be. Because not only was I running hardware RAID 5, I had spent an entire day before settling in for the long haul of permanent use by throwing as many problems at the hardware as I could think of to see how my final setup would react down the line.

You learn to fear the high pitched warning beep of server grade hardware. If server components were babies -- which is how you feel about them after you hold them for the first time -- their high pitched warning beeps are the sound of a maternity ward as played back at a Wembley Stadium concert. At a volume that The Who would consider too loud.

I pulled hard drives from the test array. I changed the order in which the drives were plugged in. Beeping all the while, the card did not let the test array fall over, and at the end of it I thought I knew how it would react in every situation that could make it fall over.

It was solid. I built the RAID.

There was one small caveat I was well aware of as I lashed the drives together. A RAID 5 system will fall over when it loses two drives, because of the way it splits its redundancy information over the array members. It’s like sliding out the middle Jenga piece from the bottom level of the stack. Your tower will fall if you pull another foundation, but you can put the piece back in.

The card I was using was quite good at this: from my testing I'd found that if I swapped an unformatted disk for any of the drives that were being used, it was only a matter of time until my card would assimilate the new drive into the array; with proper formatting and the parity information that the drive should have contained rewritten.

The problem was that the four drives I wound up using had identical serial numbers save for the last digit. They all rolled off the production line at the same time, and from the outset I had plans to do something about that.

You see, drives from the same batch are likely to fail at roughly the same time if they’ve been used for the equal time with equal ferocity. And that’s exactly what RAID 5 does. For nearly two years I'd been telling myself that one of these days I'd get around to replacing individual drives to cut down the probability of all of them dying within a week of each other and losing everything.

I suppose I could have used one of the three normal hard drives I had hooked into the motherboard, but they are all over 500GB, and because my initial setup ran on 500GB drives, no array member would be able to use more than 500GB of space. The extra just becomes a void of unusable space. And I needed that extra space for the footage I’d been shooting throughout the years. So the RAID 5 remained unchanged for nearly two years.

Having redundancy is great, except when you take your data for granted. And things get compounded even more when you get complacent about backups. I told myself “I have RAID 5. Why back up anything when I can just swap new drives in to avoid failure? I am Boris! I am invincible!”

I came home to the sound of an attention starved and beeping card trying to tell me something. I was drunk at the time. I turned off the PC, and decided to deal with it later.

I eventually discovered that two drives were offline and the array had failed. I panicked, my heart sank, and then I unceremoniously turned off my machine.

I made myself some tea and tried to console myself.

I still haven’t turned it on again. It’s too painful. It’s too soon.

God only knows when my last backup was. And the most irritating thing is that my anally retentive folder hierarchy meant that all I had to do was drag one folder, \work, to somewhere else –- anywhere else! -- and most of what I couldn’t have recreated from DV tapes and the internet would have been safe.

Let my pain be a lesson to you – back-up early, and back-up often.

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Atomic Magazine

Issue: 133 | February, 2012

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