RAID1 - can disk be used as standalone?

[Maverick2002]

Simple question:

In RAID1 (mirrored), can one of the drives be removed, placed inside an external enclosure of some sort (or plugged as a slave drive into some other system) and be capable of reading/writing data (thereby acting as a completely separate hard drive with no traces of RAID in it)?

For all the explanations of RAID online, I can't find an answer to this.

 

[RebateMonger]

While there might be exceptions, yes, most RAID 1 systems create disks that are readable separately when connected to a non-RAID controller.

Don't try to BOOT to (or write to) a removed RAID-ed drive and then try to add it back to the former (now impaired) RAID 1 array. You'll cause a mess. If you need to add it back after you've written to the drive, erase the drive and THEN add it back to the RAID 1 array (as if it's a new replacement drive).

 

[Maverick2002]

Well let's say this:



System has motherboard hardware controller, 2x drives in RAID1 (DriveA and DriveB).

Motherboard chokes. DriveA is removed and inserted into a different system with a different motherboard and used a boot drive (system drivers reinstalled as necessary to account for new motherboard). DriveB is formatted and inserted into new system as well. New RAID1 array is set up using DriveA as the "master copy".

I basically want to know if a RAID1 array can be rebuilt in another motherboard with another controller, as well as used as a sort of "system backup", aka remove the drive, save it as a backup, insert a fresh drive and rebuild array onto this new fresh drive.

 

[Maverick2002]

Hmm, maybe it's not so, got this from http://en.wikipedia.org/wiki/R...y_of_independent_disks

"Finally operating system-based RAID usually uses formats specific to the operating system in question so it cannot generally be used for partitions that are shared between operating systems as part of a multi-boot setup. However, this allows RAID disks to be moved from one computer to a computer with an operating system or file system of the same type, which can be more difficult when using hardware RAID (e.g. #1: When one computer uses a hardware RAID controller from one manufacturer and another computer uses a controller from a different manufacturer, drives typically cannot be interchanged. e.g. #2: If the hardware controller 'dies' before the disks do, data may become unrecoverable unless a hardware controller of the same type is obtained, unlike with firmware-based or software-based RAID)."

Or does this condition not apply to RAID1 setups?

 

[DaveSimmons]

RAID 1 mirroring is normally 2 identical drives with standard formatting. That wiki entry is referring to the striping and parity schemes used for RAID 0 and 5.

 

[Maverick2002]

So they're both independent of the controller then?

 

[Paperdoc]

You use the phrase, "system has motherboard hardware controller". Probably not exactly right. I presume you're talking about a very common current system which has "RAID built into the motherboard". In fact, the RAID system is software resident in the BIOS, rather than separate dedicated RAID controller hardware.

By the way, no, the disks and their data are NOT independent of the controller. Whether the control of the RAID array is by software or hardware, each RAID controller maker seems to have their own flavor and it is not common for a disk set made on one controller to be usable with another controller. In some cases, even different controller models from the same manufacturer are "incompatible". There are exceptions to this - see my next paragraph about nVidia as an example. But another way people address this is to insist on using an add-on hardware card, rather than the mobo's built-in system. The idea is that if the mobo craps out you simply get another and move the RAID controller card. And if the card fails, you buy another just like it, making sure the new one is "compatible" with the old one.

Anyway, you're talking about RAID1 in particular. I'm not positive about this, but I thought that some mobo's and HDD controllers cannot read one of the disks from a RAID1 array from another machine because they can't recognize some of the Partition Table data to understand the disk. However, some can do this, especially if machine #2 has the same mobo chipset as machine #1. In your case, check carefully into the details of what chipset your mobo has, and what the chipset manufacturer's website has to say about this question. I know that one of my machines has a nVidia chipset and their website claims that ALL of their recent RAID controller systems use exactly the same algorithms so that you can get away with moving a RAID array disk set from one machine to another (IF they both have nVidia chipsets) and it will be usable on Machine #2.

With RAID1 there is a clean way to do what you want. Read the RAID manual for your system fully. In mine there is a menu choice to break the RAID1 array. What this does is re-mark some info on the two drives so that they become independent "normal" (non-RAIDed) drives, and at least one of them (maybe both) has ALL the info on it so it can be moved and used in any other machine. Now, IF your system will do this and make BOTH drives useable independently with all their info, you could do this breakup, stash one in a safe place, and then use the second drive as a new master (along with a new third drive) to create a new RAID1 array based on the info on that master.

Even if breaking the array produces only one disk with all the info intact, you could do something similar. Break the array, then remove the disk with all info. Install a third disk and create a new array, empty. Re-install the disk with all data as a "normal" disk, then copy everything over to the new array. Un-install the original disk and stash it in a safe place.

However, if your original aim was to make a good backup, this seems a complicated way to proceed.

 

[Maverick2002]

Thanks a lot for the detailed explanation. The original intent is not to make a backup, but rather have redundancy in case of a hard drive failure. Since this introduces another variable (motherboard failure), it seems like it would be a good idea (like you said) to get an independent RAID controller card (and a spare or two) and use that to set up the array.

 

[corkyg]

All technical stuff aside, I can answer your question with a firm "yes." I have a RAID1 array for all my data storage. I have backed that array up to a single external drive. (Acronis TI sees the array as a single drive.) I have upgraded the array by replacing each drive and then rebuilding the array and cloning the data from the backup external. Then I took one of the array's drives and put it in another computer as a single data drive. No problem at all.

 

[Maverick2002]

Corky, thanks for the info, that's not quite what I meant though. I meant physically removing a drive from a RAID1 array, plugging it into an external enclosure (or another computer) as a standalone drive and accessing data on it. THAT doesn't appear to be possible. What you mentioned is perfectly fine though.

 

[corkyg]

I should have expanded that. I have done that and it works. Each drive of a RAID 1 array is a duplicate of the other. They can be removed from the array and run as single drives. The only thing that makes them RAID is the RAID controller.