My earlier post on Windows Home Server’s Drive Extender vs RAID, a lot of what I said was a good example of somethin’ my pappy once told me:
"Good judgment comes from experience, and a whole lotta that comes from bad judgment."
Well, rest assured that I’ve had my share of bad judgement, as I’m sure others have, given some of the feedback I’ve received. Charlie pointed out to me some of the other really good reasons why you’re better off not going with RAID5, rather than just using Drive Extender:
While RAID5 hardware is fast, it is also pretty much universally incompatible. In other words, if your RAID5 controller fails you will have to find an IDENTICAL controller to replace it or your array will be unreadable.
For those playing along at home, this is bad. If you think your data is valuable enough to keep around, and you’re worried enough about failure that you’re going to do something about it, think about what else will fail–not can, but will— hard drives, controller cards, motherboards, ram, network adapters, power failure. I’d mention the possibility of meteor strikes, but … I’m gonna play the odds with that one.
When I think about the how each of those failing is going to affect my ability to even recover data, the controller card is a nasty wildcard. There is no standard layout for how each controller card uses all that storage, and it’s going to be needing replacement with the exact same controller.
All drives in a RAID5 array have to be the same size.
Hey sure, no problem. I can get 750 gb drives the same size in the future… Uh, except there is no guarantee that the drives will be exactly the same size, (even if they are labeled the same), and it’s possible that other changes in the future could render them so obsolete, that it could be hard to even source drives of a particular size.
Furthermore, as you progress into the future, with Drive Extender, you can simply buy any size of drive that fits your budget, and add it to the server. No worries about how big, what brand, how fast, etc.
Drive Extender gives you the flexibility to NOT duplicate files that don’t need to be duplicated (making it MORE efficient than RAID 5 in some cases).
And this, is a really really good point too. Sometimes, I want to have data that I really don’t care as much about, or I’m less worried about it being backed up and online. With Drive Extender, you can mark some content as not requiring duplication. Like maybe TV shows I’ve recorded on Media Center. Or those videos of my in-law’s trip to Cleavland. You know what I mean.
RAID5 rebuild times with a single drive failure are often as long as your 3.5 month ordeal of recovery!
Well that’s certainly true–I took all summer to restore my data, and I had no idea until I got it back if I would.
RAID deals at the block level and thus knows nothing about the interesting file information (metadata, etc…). Thus it will NEVER be able to be smart about your storage. But Drive Extender is file based and tons of innovation can happen (will happen!) leveraging this fact.
This is the point that I think is even more important, and yet so many folks will either ignore or not really understand. RAID is a system of aggregating independent disks and presenting that larger volume that to the OS as a single large drive. It works at a block level, meaning that your RAID system really knows nothing about files, just blocks. And because it’s unaware of that, there is so many optimizations that can’t be done with it. With file-level data redundancy, the system knows a lot more about it, and can begin to make decisions that would be much more beneficial. Think, down the line in a couple years, as I add a few more hard drives to my growing server–which already contains drives that are connected by Firewire, SATA, ATA and USB (*sigh*)–it’s possible that the technology could realize that I rarely ever touch some kinds of data (or specifically, some types of data) and it could migrate those files to the slower media, and keep the faster media for things that need it.
Now, my momma said that I should always end by sayin’ somthin’ nice, so I’ll leave ya with this:
So is there anything good about RAID5 or are you just some sort of once-scorned-RAID-hater?
I’ve said it before but it bears repeatin’: RAID–in general–is great for performance, and RAID5 adds to that, availability. My desktop at home has 1.4 terabytes of space, striped (that’s RAID1). My desktop at work has 2.8 terabytes of storage, again, striped. Sure, sure, with 4 750 gb drives, and using striped storage, I’m subject to failure at 4x the rate I was before (probably more, cowboy math ain’t that great… :D). On those systems, I’m not leaving anything there that I can’t afford to lose, either because I’ve backed it up, or it’s recreate-able.
But WHOOOOOSH, it sure goes fast!