Question about Linux Software RAID

[MGMorden]

Hey guys. I've got a fairly basic question here.

I've recently purchased an external drive housing, a SATA card that supports port multiplying, and 4 2TB hard drives. My intention is to setup a RAID5 array for a big file repository on my Linux desktop (Ubuntu 10.10).

Setup seems straightforward enough - I've got the RAID array configured and it's currently building (should be finished in about 14 more hours ).

My question though is about the recoverability of such an array in the event of the main system drive failing. Most of my experience setting up RAID arrays has been with servers where the array is configured in a hardware card's BIOS (and is hence outside the scope of the OS). Since this is software RAID, I'm assuming that there is some type of configuration defining the RAID stored somewhere.

If the drive holding that information crashes, gets accidentally reformatted - whatever - is it possible to recover the RAID array again without data loss? Are there any specific configuration files that would assist in helping me restore it in such an event?

Thanks.

 

[Nothinman]

The RAID superblock is replicated as well to avoid that, but if you setup the array with mdadm then you should already know where to go to replace a failed drive, back to mdadm. There is a config file in /etc/mdadm/mdadm.conf, but most of it's optional as the array information is stored on each drive.

 

[skyking]

Correct me if I am wrong, but What Nothinman means is, if your OS desktop drive fails but the array is fine, all you need to do is rebuild your desktop, add the mdadm package and mount the device.

 

[Nothinman]

True, you should be able to plug all of the drives into any machine on any ports and the kernel and mdadm should find and bring up the array. I thought he was thinking that the array config is only on one drive in the array, which isn't true.

 

[MGMorden]

I thought he was thinking that the array config is only on one drive in the array, which isn't true.

Kinda close. I figured that the array configuration was stored on a drive that wasn't in the array (ie, my system drive that is separate). Just wanted to make sure that if that was the case that I was backing up that configuration somewhere in the event that I reformat the system drive but wanted to preserve my raid array.

Sounds like this won't be an issue. I guess one of the downsides of easier admin tools is that it hides so much that you don't learn as much as you used to. Once upon a time I would have dug into this pretty good, but I was able to get the array setup with 10-12 mouse clicks, which left me kinda wondering how it actually all worked .