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RAID - Need advice understanding what would be best for me.

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April 3, 2010 12:05:26 PM

Roughly two months ago I built a new computer with three 1.5TB drives and installed Windows Home Server to use it as a media server. I was very happy with how things were going until two weeks ago I discovered that one of the data drives had a lot of bad sectors. I managed to salvage most of the media off of it before I RMA’d it but I lost a good chunk. The other data drive was full so when I transferred all the salvaged data it was written on the system drive.
Yesterday I started transferring 250GB worth of mp3 files from my main computer to the server and left to attend to something else. 20 minutes after I started transferring I went to watch something on my HTPC in the living room which pulls media from the server but there was no media to be found. I went and reset the server without bothering much about it and went back to the living room and waited for it to boot with no avail. I went back and turned the screen on to see that one of the drives was having problems in BIOS. I managed to boot it up eventually and ran chkdsk with bad sector detection on. It took several hours to finish and I wasn’t there to see the result. When I logged on the WHS console I saw that the system drive had 392GB worth of system data. I don’t know what that data is supposed to be but it shouldn’t be there. I started transferring files and the transfer rate was in the Kb/s for several minutes. I would stop and start again to see if something would change. Still nothing, transfer rate was very slow. So I just left it there for a while to see what would happen. After several minutes it reverted back to normal transfer rates (more than 20Mb/s). I know there’s something wrong with the drive but since I have all the data backed up somewhere I left it there for now and started thinking that this might not be a good solution for me.
I’ve started reading about RAID and all of its different configurations. I’ve never had any experience with RAID so my knowledge is very very limited but from what I’ve read I think that building a RAID array with redundancy would be the best solution for me since I value my media. I don’t care one bit about performance; all I care about is the safety of my media. I see 3 possible solutions, RAID 5, 6 or maybe even 1+0, please correct me if I’m wrong (I’ve excluded 0 because although I think it’s the safest it also eats up too much space for my liking). I can’t decide which would be better suited for my needs. Is it harder to build one array compared to a different one? Is it more difficult to build an array with more hard drives? Does hard drive space matter? Can I add drives as a I go or do I need to decide how much space I will need and have all the drives ready? That’s one of the features I absolutely love about WHS, adding drives as I go. Will RAID work in WHS? Would I be better off with a different OS? How much space will be used for redundancy? What about hardware? What kind of hardware will I need depending on what I choose?
I know I have a lot of questions. This is probably a long term project and I need to be sure I do it right. Once I set it up I don’t want to bother with it much like I’m doing now with my current setup. Most importantly I want my data to be as safe as possible without sacrificing too much space.
Any advice would be greatly appreciated.
a c 415 G Storage
April 3, 2010 6:36:38 PM

It sounds like you're top priority is data security. If that's true, then you can't use RAID 0 because it provides NO redundancy.

RAID-1 is an excellent choice - you'll have two complete copies of all your data. But it's expensive in the sense that you only get to use half the space you've purchased (i.e., with two 1.5TB drives you only get 1.5TB of usable space).

RAID-5 is the cheapest redundant organization (you need to buy 1 extra drive), but is probably not the best choice because if you loose a drive you can only recover if you can successfully read EVERY other block on the remaining drives. As you've seen, if blocks go bad then you've got a problem.

RAID-6 is better than RAID 5 because if you loose a drive you'll be able to recover your data unless you get bad blocks in exactly the same place on the remaining drives - an unlikely scenario. With RAID-6 you need to buy two extra drives for the redundancy data.

If you decide to go ahead with a RAID solution then it's very important to test your failure and recovery procedures BEFORE you commit important data to the RAID set. If you have a drive failure the last thing you want to be doing is to be risking your data while you learn how to do a recovery by trial and error.

When figuring out your recovery procedures pay special attention to how you'll identify WHICH drive has failed - if you replace then wrong one then you're hooped.

Don't forget about backup. RAID protects against drive failures, but not against viruses, accidental deletions, power hits, theft, disaster, etc. etc.
May 12, 2010 3:45:56 PM

Compare RAID levels:

RAID 1—The same data is written to 2 drives. If one drive fails, your data exists and is readily accessible. The useable capacity with be half of the physical capacity of the drives.

RAID 0—Careful, this offers no additional protection. Data is simply written to multiple disks as if they were one. If one of the drives fails, all data is lost. Usable capacity will be the same as the physical capacity of the drives. RAID 0 is not recommended for data protection.

RAID 5—Data is written across all the drives along with extra information (called parity) such that your data can be retrieved if any one of the set of drives fails. A RAID 5 storage device requires a minimum of 4 drives. Usable capacity will be the physical capacity less one drive.

RAID 6—Data is written across all the drives along with parity information such that your data can be retrieved if two of the drives fail. A RAID 6 storage device requires a minimum of 4 drives. Usable capacity will be the physical capacity less 2 drives.

RAID 10—A combination of RAID 1 and RAID 0. In this case, data is mirrored and then striped across all the drives. Usable capacity is half the physical capacity of the drives.

Borrowed from Iomega (http://download.iomega.com/com/nas/pdfs/raid.pdf)

Good luck!

a b G Storage
May 28, 2010 10:17:48 AM

Bit of a bump but, if you're still out there, try z raid.

Z raid is like raid 5 but with some important upgrades. The type of data corruption problem you had on your whs box should not happen using zraid. It could happen using raid 5. With FreeNAS you could build z pools which, although not expandable in themselves, are easily striped later and can even be striped with different sized pools. Look into it or bump this thread for more.
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