Degraded Raid-5 array

[Natursvin]

Hey, i currently have raid 5 array consisting of 3 harddrives and then i was gonna add a nother one whit the OCE function. But while the array was beeing rebuilt whit the new harddrive the harddrive failed. Then the LSI-raid card rebuilt the array again whit the original 3 drives. As far as i can see i havent lost any data but now the MegaRAID managers say the the array is degraded but it does not state which drive or any other information as far as is can see.

 

Any thoughts?

[Vitalius]

Oh! Oh oh! I think I know the answer! Pick me! Pick me! 

Questions: What specific model of hard drives are they? How much data was stored on them? How old are they? These are all very relevant questions to figuring out whether you did what I think you may have done.

[TheProfosist]

Well its degraded because you don't have the redundant drive anymore.

[Natursvin]

Oh! Oh oh! I think I know the answer! Pick me! Pick me! 

Questions: What specific model of hard drives are they? How much data was stored on them? How old are they? These are all very relevant questions to figuring out whether you did what I think you may have done.

The hard drives are seagate barracudas 3tb. The amount stored was alittle over 5tb, the original ones are under 6 months old and the one i tried to add was over 2 years old.

[Natursvin]

Well its degraded because you don't have the redundant drive anymore.

But can you still read from a raid-5 array if you are missing a drive?

[Vitalius]

Well its degraded because you don't have the redundant drive anymore.

 

Possibly. I don't know specifically how attempting to add a drive to an array, then failing and reverting back goes, but I do know he either is, or could be soon facing an issue with RAID 5.

The hard drives are seagate barracudas 3tb. The amount stored was alittle over 5tb, the original ones are under 6 months old and the one i tried to add was over 2 years old.

So they aren't NAS drives? 

Well, that's not good. In fact, that basically defeats the entire purpose of RAID 5. For the full explanation, read this post by me.

Using normal consumer grade drives with parity RAID (that's 5, 6, & 7) is a bad idea. It is so because when you try to rebuild the array, you are likely going to run into issues where read errors occur. The more data you read, the more likely these issues are going to come up. It being 5TB of data (not counting parity data which is probably another 1-2TB), means the risk is very high.

Basically, your RAID controller is probably saying your drives are failing when they aren't. This is usually because they hit a section of the disk that is hard to read and took too long to do it. This is bad. It basically means you can't rebuild your array. Rebuilding your array means reading and writing tons of data. The more you do that, the more read errors you will hit. The more read errors you hit, the more likely you are to lose your entire array by way of attrition.

You can probably still access much of your data, but as time goes on, it's going to get worse and worse (matter of probability). And there's not really much you can do about it. I hope you have good backups. 

If I were you, I would try and copy off as much data as you can to some other storage medium that doesn't use Parity RAID, or at the very least uses Parity RAID along with NAS/Enterprise grade drives. 

Sorry. You might get lucky, but odds are that this is your problem and it's not something you can easily fix. Or recover from either.

 

But can you still read from a raid-5 array if you are missing a drive?

Yes, you can. That's the point of RAID 5. You can lose 1 drive and be perfectly fine... until you lose another one, then everything is gone.

[TheProfosist]

But can you still read from a raid-5 array if you are missing a drive?

Yes as it's on degraded. All the data is still safe but if another fails at this point your SOL. This is why I always have at least 1 extra drive for my raid arrays.

[Natursvin]

okay thanks for the info i have lots of eksternal bakcups so i think it going to be fine.

[Vitalius]

okay thanks for the info i have lots of eksternal bakcups so i think it going to be fine.

Good, glad it can end well for you.

If you don't want to have this issue again in the future, either never use Parity RAID (5, 6, or 7), or use it with NAS/Enterprise grade drives (Seagate NAS drives, WD Reds, Hitachi Deskstar NAS drives, WD SE/RE drives, etc). Then you won't have to worry about this issue (I'm still assuming it's the issue I'm talking about, as I can't 100% verify it, but it's very very likely that's it). NAS/Enterprise drives have technology in them that prevents this from happening.

[TheProfosist]

Good, glad it can end well for you.

If you don't want to have this issue again in the future, either never use Parity RAID (5, 6, or 7), or use it with NAS/Enterprise grade drives (Seagate NAS drives, WD Reds, Hitachi Deskstar NAS drives, WD SE/RE drives, etc). Then you won't have to worry about this issue (I'm still assuming it's the issue I'm talking about, as I can't 100% verify it, but it's very very likely that's it). NAS/Enterprise drives have technology in them that prevents this from happening.

Na the drive probably just took a crap. i use non enterprise grade drives in all of my arrays, you just have to plan for them to die at some point them RMA them. The thing your thinking about TLER and is absent from WD Green drives but that is the only drives to my knowledge but it could also apply to other companies "greeen" drives.