Backing up RAID, and is it bad to use green drives in RAID?

[rawdawg]

I currently have a 2x 1TB = 2TB RAID 0 from OWC. I use it on my MBP with a Sonnet Pro eSATA expresscard which delivers to me ~180/MBps peak speed, not bad.

In the future I was thinking about upgrading the drives to 2x 2TB drives to make it 4TB. Or even better was thinking about getting a 8TB RAID 5 (4x 2TB). My problem is backing them up. The RAID 5 would at least have redundancy but I'm confused about backing them up.

Since currently I have a 2TB RAID, I need to have a 2TB drive to back it up. If I wanted to make my RAID setup larger (i.e. 2x 2TB = 4TB RAID 0) then how would I be able to back that up on one drive (since there are no 4TB drives out). Would my only option be to buy another RAID 0 and set them up together as a RAID 0+1?

In this effort, I have currently bought a dock with a WD Green 2TB drive. I thought I could start with this one and in the future I could buy the identical 2TB drive and upgrade my current setup..... In further down the line buy 2 more and consider changing the setup to RAID 5 (with a new OWC case).

The time has come for me to purchase another 2TB drive and I just realized my first one was a WD Green drive. I'm not so worried about performance speed being slighting decreased by the Green drives since my bottleneck is topped at ~180MB/s with my expresscard. But does anyone know if the IntelliPower feature which "provides variable rotation rates in order to conserve power" could cause issues trying to set them up to work together in a RAID?

I know WD makes 'real' RAID HDDs that happen to be expensive. I would not buy this anyhow since I'm on a budget. For those who object to this consider that OWC already ships their RAID setups with cheaper non-enterprise class HDDs. But if these Green drives would cause considerable other issues I would like to buy a different 2TB drive and start over accumulating them -- my first 2TB Green drive would be put to another use and I'll wait for next time to buy a matching drive for use in a RAID.

 

[m85476585]

The way the SATA protocol works is the controller waits for the disk to acknowledge that the data has been written. The RAID controller will wait for each disk to successfully write some data before continuing. If it just fed a continuous stream of data to both disks, the array would fail any time any disk had a correctable write error, and it would not be possible to have arrays with dissimilar disks.

You might still run into issues with the fact that those drives use standard firmware not optimized for RAID. That can cause problems if one disk gets an error, it might spend too much time trying to fix it, making the controller think the disk is bad or has failed, when it is really OK and just has a bad sector. I don't have any experience with RAID at all, or non-RAID vs RAID disks, though. Plenty of people use regular disks for RAID, though.

I think I read one review that said the "green" disks don't actually seem to vary their rotational speed. They just run at something like 5900RPM all the time. Maybe newer ones are different.

I think the whole "green" disk thing is a gimmick to sell slower disks. A green disk might save a couple watts compared to a regular disk, which is really insignificant when the whole computer might use 200-300 watts (typical desktop PC).

 

[ayeying]

I'm using dual drives in RAID. I haven't seen any issues.

 

[rawdawg]

Thanks for the feedback everyone.

It's good to see another person has used these Green disks in a RAID setup. Guess that means there shouldn't be much to worry about.

Am I correct about backing up RAIDs? I seem to be worried about it. It seems rather difficult because the easiest way would be if you can fit the whole array on one disk, but once your array is larger that 2TB how do you back it up? Seems you would need a RAID 0+1, or go through the trouble of backing up portions on separate disks.

 

[skh]

Is it really necessary to backup a RAID5 array? If one of your disks fail you can still recover from it.. only if two failed at once would you be in trouble. Most people use RAID5 as their form of redundancy/backup.

As for your remarks about the Green drives, personally for a backup / media drive I highly prefer them. They can spin down when not in use, prolonging their life. I've had great luck with this samsung one.

 

[KnightWRX]

Is it really necessary to backup a RAID5 array? If one of your disks fail you can still recover from it.. only if two failed at once would you be in trouble. Most people use RAID5 as their form of redundancy/backup.

RAID is not a form of backup, as any sufficiently informed admin will you tell you. There are a lot of scenarios raid doesn't cover that can result in loss of data.

Home users though don't really have the capacity to backup such big arrays though. In the enterprise, you'd just use a couple of tapes and call it a day. The problem is that the tape drives costs are prohibitive if not the media costs and backup software can be a pain to work with.

So just cross your fingers that you don't lose data through manipulation errors or software errors and replace failed drives as soon as possible.