RAID vs Spanned & Mirrored

[Muther]

I'm building my new system this week and I am still exploring my options for storage.

I have an SSD for Win7 and 4 3TB drives. I intend to keep a mirrored copy of my media, so 6TB/6TB (except if I use RAID5). I'm not overly concerned with speed, more with redundancy. My options seem to come down to 1) A RAID configuration, or 2) Two spanned volumes using robocopy as a daily scheduled task.

It is crucial for me to have each mirror as a single drive letter. This has to do with my extensive use of shortcuts throughout the folders.

I want to step up from manually backing up my media. I started out intending to use RAID 10. I've never used RAID, so I've been reading a lot about it. I must admit I'm a bit put off by RAID rebuild times. I just do not see the great advantage to RAID configurations for my use. Someone might tell me what I'm missing... I can understand other uses where instant redundancy would be important and maybe the speed increase of stripping too. But I just want a big old disk and a mirrored copy... why RAID?

Spanned volumes seem to get bagged on for the possibility of losing data on both disks if one disk fails. Does this matter is I have a mirrored copy? Am I better protected in RAID? With RAID I replace the drive and rebuild, with spanned volumes I replace and mirror. In either scenario if I lose 2 disks at once I could be FUBAR.

I guess all I'm thinking is RAID seems to be all the rage... But I'm not seeing the great advantage for storing my media. Please, tell me what I am missing.

 

[manofchalk]

There is a difference between Backup and Redundancy, each of your solutions does a different one.

RAID is good for redundancy, protecting your data in the face of a drive failure. However if you delete something or it is corrupted via software, its gone, RAID doesnt protect you here. Also in this case with a RAID10 array, it also gives a fairly decent performance boost.
Your mirrored spanned drives does offer you redundancy as you can recover from a drive failure, as well as backup as you can recover lost data assuming you get to the mirrored copy quickly enough. You lose the performance boost though.

One idea I had is that you have two RAID0 arrays, effectively making two 6TB disks with increased performance, and use one to back up the other. This will get you the best of both worlds.

 

[Muther]

There is a difference between Backup and Redundancy, each of your solutions does a different one.

RAID is good for redundancy, protecting your data in the face of a drive failure. However if you delete something or it is corrupted via software, its gone, RAID doesnt protect you here. Also in this case with a RAID10 array, it also gives a fairly decent performance boost.
Your mirrored spanned drives does offer you redundancy as you can recover from a drive failure, as well as backup as you can recover lost data assuming you get to the mirrored copy quickly enough. You lose the performance boost though.

One idea I had is that you have two RAID0 arrays, effectively making two 6TB disks with increased performance, and use one to back up the other. This will get you the best of both worlds.

That is actually a very attractive idea: Two RAID0 and backup... Thank you, manofchalk. I am not super clear on the difference between backup and redundancy, except where there is a gap between backups when data can be lost... or recovered, depending on what happened. Backup seems preferable - at least in my case.

I've been messing around with the Windows command line tool, Robocopy, for the last couple hours and I am impressed. A lot of switches to figure out, but pretty fast considering the amount of data.

I keep thinking someone is gonna jump in here and make me an idiot by pointing out some huge, obvious advantage to RAID....

 

[manofchalk]

Redundancy is that your storage system is fine if you hit a drive failure. The simplest example would be RAID1, which is two drives mirrored in real-time. If either one fails, you still have the other with all your data on it and can start back up again immediately with no data lost. However if you delete something, accidentally format the partition, its gone on both drives as its a real-time mirror.

Backup is what you expect it to be, its a copy of the drive (or just important data) with a time delay. If you delete something or otherwise mess up the primary drive, you can always recover from the backup drive, assuming it was there the last time it backed itself up. Most of the time people only back up important stuff, so in terms of "get my system up and back the way it was" redundancy, backing up offers nothing, it only minimizes data loss.

Since your backing up the whole partition, if your primary partition fails then you have only lost the data generated since the last backup.