Disk Failure - RAID 5....uh oh!

[Wandering_Youth]

Well one of my hard drive in my RAID 5 array has failed making my system slow, unresponsive, problematic etc. I removed the failed HD and hooked it up to another computer to run some test to see if it is truly dead.

Quick question, how do I make the RAID 5 rebuild itself. I understand that I need to plug in a new HD, but where do I go to intialize the rebuild or does it do that automatically?

RAID 5 Array (Software RAID - Intel Z77 Chipset - Gigabyte Motherboard):
2x 1TB Hitachi HD
2x 1TB Seagate HD (1 Failed)

Surprisingly, when I removed the failed HD, my RAID 5 array works just fine and all my files appears to be intact and usable. I didn't expect that! I thought RAID 5 spreads all the necessary data to all the hard drives in the array so it could be rebuilt if one was to fail. I didn't know the array still works when it's missing a hard drive.

[SeijiSensei]

RAID 5 spreads the data across N-1 of the disks and writes a "parity" record on the last one (=1 if the sum of the equivalent bits on the other drives is odd, otherwise zero). The array can survive the loss of one drive, but typically not more than that.

Usually hardware RAID systems handle rebuilding the array themselves. I'm not sure I understand why you think your system has "software" RAID. In Linux, for instance, software RAID means that it's handled by the operating system and no hardware is involved. Some systems use what's called "fake" RAID which is a strange mix of some hardware support and a proprietary OS driver to make it work. That's fine if you run Windows where the driver might exist, but useless if you run any other OS.

Have you tried simply inserting a new disk into the array and watch to see if it gets rebuilt? You need to do this soon in case another drive fails. Then you'll never be able to retrieve the data again.

Remember, too, that RAID is not a substitute for backups. I learned that to my dismay some years back.

[spikexp]

Replace it fast before another drive break.
With raid 5, you can only loose one hard drive safely, more than that and you loose everything.

The reason you can still use it, is that the missing hard drive is "emulated" with the data from the other drive.

For the rest, like SeijiSensei said.

[Wandering_Youth]

Originally Posted by SeijiSensei

RAID 5 spreads the data across N-1 of the disks and writes a "parity" record on the last one (=1 if the sum of the equivalent bits on the other drives is odd, otherwise zero). The array can survive the loss of one drive, but typically not more than that.

Usually hardware RAID systems handle rebuilding the array themselves. I'm not sure I understand why you think your system has "software" RAID. In Linux, for instance, software RAID means that it's handled by the operating system and no hardware is involved. Some systems use what's called "fake" RAID which is a strange mix of some hardware support and a proprietary OS driver to make it work. That's fine if you run Windows where the driver might exist, but useless if you run any other OS.

Have you tried simply inserting a new disk into the array and watch to see if it gets rebuilt? You need to do this soon in case another drive fails. Then you'll never be able to retrieve the data again.

Remember, too, that RAID is not a substitute for backups. I learned that to my dismay some years back.

I thought software and fake RAID meant the samething. Thanks for clearing that up. Do I need to use the exact same hard drive size and brand for it to work?

[SeijiSensei]

Brand, no, as you have already seen. But size, yes, the new drive needs to be at least as large as the existing ones. It might be possible to add a 2 TB drive that you have partitioned into two 1 TB halves, assign one of them to the array, and format the rest as a normal drive. That would depend on the capabilities of the RAID system you're using. The easiest solution is to buy another 1 TB drive.

[Wandering_Youth]

Any opinions on what software is usually the best for backups? I'm looking for something that is fast, I hate backing up my files because it usually takes hours and I am usually using my computer for other things during the backup process or I leave my computer on all day while I'm at work, but that's a waste of electricity.

Specifically is there a backup software that can selectively only backup changes in a source drive and not have to backup the entire drive every single time. Kind of like synchronizing a source drive to a backup drive.

[spikexp]

I use FreeFileSync for my backup on external hard drive, there is probably better, but it get the job done.

[SeijiSensei]

I'd take a look at this: http://www.aboutmyip.com/AboutMyXApp/DeltaCopy.jsp

It uses rsync, which has become the standard command-line backup utility in the *nix world. It's very cleverly designed to minimize the amount of copying involved. The author is a very smart Australian fellow named Andrew Tridgell who was also responsible for creating "Samba" which emulates a Windows file server on Unix platforms.

I have rsync scripts that run nightly to make backups over the Internet. I back up my public servers to a machine in my house along with my local file server where I keep all my work and email.

[0utf0xZer0]

I've found Microsoft Synctoy gets the job due with minimal fuss, though I haven't played with the scheduling capabilities - those apparently require using Window's task scheduler.

[Wandering_Youth]

Thanks for the opinions, I'm trying out Robocopy and so far I like it. I finished checking the hard drive that supposedly died, but it seems to work fine. I plugged it back into the array and it rebuilt itself in 3 hours. However, I'm wondering if said hard drive is near the breaking point and I should go buy a new hard drive.

[SeijiSensei]

Originally Posted by Wandering_Youth

I'm wondering if said hard drive is near the breaking point and I should go buy a new hard drive.

Use smartmontools. It's free and cross-platform. Here are the installation instructions for Windows. (Linux users can just install the "smartmontools" package from their standard repositories. Here's the documentation for Ubuntu.)