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Monday, May 18, 2009

Jessica Cambensy Sexily Compares RAID 5 and Windows Home Server

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Hey, Jessica here. Blogging in for Anthony for this week's daily dose of technical heaven. Today, I'm going to run across WHS (Windows Home Server) and its perks against the ever elusive topic of going RAID5 in a consumer's home tech environment. First off, let's talk about the Drive Extender feature used on WHS.

Windows Home Server Driver Extender basically gives you 3 big perks. First, it functions with multi-disk redundancy so that if any given disk fails, data is not lost - it's already be duplicated somewhere else. Secondly, it has arbitrary storage expansion by supporting any type of hard disk drive (Serial ATA, USB, FireWire etc.) in any mixture and capacity. Finally, you get a single folder namespace (no drive letters). This is big on minimalist technophiles, I've heard.

So, lets compare the two a little more thoroughly, shall we? I'm going to run through a couple of questions I've heard through my hundreds of hours scavenging the internet. Here's a few sample ones I'll be answering in due time: Isn't RAID better than Drive Extender? Why should I use Drive Extender instead of RAID? Which RAID card should I buy? How good is software RAID5?

First off, I would strongly suggest against going for any software-based RAID 5 solution. There's a gap as wide as the Grand Canyon between software RAID5 and hardware RAID5. Software RAID5 is slow. Damn Slow. Meanwhile, hardware RAID 5 runs fast. Zippity fast. So fast, that if two drives fail, you'll be losing your data faster than you can say, "Hey baby, I like that dress on you."

My selfish arrogance aside, it's clear that RAID5 is geared towards performance and availability. It's not about data integrity. If you want your data to be safe, replicate it. Back it up. Put it in a jar. A jar far away from your main personal computer. Keep in mind this - even if you use RAID5, you're still going to need to back it up. RAID5 is designed so that an event of a single drive failing, it will preserve your data and make it available (but slower) until you get another drive in place, when it will rebuild the missing volume.

So what happens exactly when one drive fails in RAID5? If you're not there, the system will try to rebuild itself. This causes all of the drives to get real busy and when it does this, the chances chances of losing a second drive go through the roof. When that happens in RAID5, you're completely screwed. I'd also like to add that a contributing factor is the fact that people tend to use the same brand of drives when setting up the initial array. This means a higher possibility of a faulty batch, since they were purchased at the same time.

My personal experience with RAID5 goes a little something like this. I had a server running RAID5 at home, it ran perfect for over a year (actually, close to two). One night after I went to bed, a drive failed. 3 minutes later another failed. This was a 2 terabyte RAID array.

I came down in the morning to my worst nightmare. Every bit of "valuable data" I had in the world was now gone. In desperation I scoured the internet, and finally found a piece of software that (for $40!) could recreate every file that I still had data for, if not a little slowly. I rushed out and bought 3 750gb drives, and started to restore everything I had lost. The restore process took a ridiculously long 3 1/2 months, running full time, around the clock. The good news is that I was able to get one of the failed drives spinning again, and I lost a total of one file.

What did I learn? I learned RAID5 doesn't back up my data. Sadly, I thought it was safer. Worse than that, it was actually less safe. A single drive failure would have meant nothing. Add another drive, and keep chugging. Potentially, it may have taken a few hours to rebuild the lost volume, but I could have been using it while it did.

A second drive failure would have meant I was offline for a little while for it took to restore - if I actually had a backup. Still, not bad, considering that would have been less than the 3.5 months. But a two drive failure (which is fairly likely given all the variables) - without a backup - is a nightmare.

If you value your data, replicate it. I'm now using WHS with 6 250gb drives and 3 750gb drives, and the data that I value (pictures of myself, etc) is replicated as per specific settings set in the OS. The really important stuff (photos of Anthony, etc) is foldershare'd to a friend’s house and vice versa, giving us both off-site backups. While not very 'space efficient,' I can at least deal with a drive failure.

Now let's go over the other two popular options: RAID1 (mirroring) is the only RAID where a failure doesn't increase drive activity drastically since reads just going to one drive now, instead of one. For RAID0, the focus is purely speed. For example, if I were to walk down an alley by myself at night in one of my low-cut miniskirts in order to get to my flat faster, I'll be sacrificing safety in order to reach my destination at twice the speed. I would only use this for my PC desktop at home, where I want it fast and with nothing except my OS is running on it. All of my important data, of course, goes to my WHS.

My final bit of advice is to know this: If you're using hard drives, you will eventually experience a drive failure. Not 'might,' but will. How badly you are affected depends on your choices. So, determine how valuable your data is. At the price you pay per GB these days, it's stupid (and a turn-off for me) to try and and play it cheap when it comes to hard drives. Disk space is cheap. The stuff you store is not.

I think the victor is clear in this little essay of mine, but feel free to add your own two cents in the comments. I'd love to hear from you. And maybe, if you're tech-savvy enough (like me), you'll get a little invite from me to take a trip to my local Fry's Electronics.

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