RAID5 is Dead

January 27, 2015

 

A few weeks ago, I asked if your backup solution was sufficient and David shared a bit about "unrecoverable read errors."   

There was another piece of the story that I wanted to share, though.

What is RAID5?

Without getting into a lot of technical gobledygook, RAID 5 is a form of disk backup that requires a minimum of three disks and all but one of them must be working for the RAID array to be functional.  

 

How RAID5 Fails

We had this set up at our home for pictures, MP3's and such and had two drives die almost within days of each other, so you really need to stay on top of the health of the drives. If you don't, you stand a change of losing your data.

Here's how David explained it to me:

...in RAID 5, if you have a disk failure and you replace the drive, it tries to rebuild the new drive by reading the differences between the remaining drives. If one of the remaining “good” drives gets a URE, it will not be able to rebuild the array and effectively crash the entire array and you lose all your data. All because one bit on one drive could not be read.

 

Unrecoverable Read Error, RAID5, and Your Backup

As I mentioned, we have used RAID5 in our NAS at home.  This is where I store all of my homeschool materials, photos, MP3's and ebook library among other things.   It's the home equivalent of a file server at the office.   And that's fine for my personal files.

If the drive is a data drive and the one bit that cannot be read is in a Word document or other small file, it’s probably not the end of the world, you’ll lose some valuable data, but not everything.

If you use RAID5 in your backup, you could be setting up your data to fall victim to the perfect storm.   If the one bit that cannot be read is a drive that holds backups, it's a much bigger deal.   Backup files are typically large files that contain lots of data. If it cannot read even a portion of the backup file, then the whole thing is lost. It could be devastating if you need to restore data and that’s your only backup.

 

So what?

So what does this mean for you?   Well, I would take the opportunity to review your server and backup processes, especially if you are using RAID5 or you have no idea what you are using.   Don't wait until a hard drive crashes leaving you in the lurch.   Take some time and make sure you are good to go!