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I need to setup RAID1 (software/hardware).

I have a 1TB (no space left), can I buy a new 1TB and setup RAID1 successfully without a remote chance of loosing anything on the existing 1TB, as I got it back from data recovery now and that wasn't cheap.

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I am not aware of a process of creating a RAID volume that preserves the content of any RAID member. Usually, you backup, create volume, restore. –  Oliver Salzburg May 23 '12 at 17:41
+1 - It's not what I want to hear, but what I thought. –  neolace May 23 '12 at 17:45
I belive with a software-based RAID you wont need to, but with a hardware RAID I don't know but I also don't think so it is a requirement. But as I'm not sure about that and I don't find refferences, I would reccomend you to read the manual of the desired solution. By the way, interesting question, +1 –  Diogo May 23 '12 at 17:45
You do understand that adding another HDD in a RAID1 setup won't increase the amount of space you have correct? –  Ramhound May 23 '12 at 17:47
@Diogo: Software RAID is a great point! Maybe you could create a new RAID volume with mdadm with a single member disk. Then add an additional RAID member. –  Oliver Salzburg May 23 '12 at 17:48

3 Answers 3

up vote 3 down vote accepted

What do I need to set up RAID?

A Fresh Backup (existing data only): If you're installing and configuring hardware RAID on a fresh system with no OS (your best option), or are adding disks for a separate array, skip this. Otherwise, back up your important data. Best practice is to have three copies of your data: the original, a backup, and a backup of the backup, preferably offsite.

If you have existing data that you want on the array, you'll need to back it up, then restore it from a backup you make before creating your array--a process that writes new data to your hard drives regardless of what's there. This is not necessary with Windows software RAID 0, however, it's far faster than letting Windows re-sync (copy the data to) the mirror in the background.

Transferring an existing operating system is tricky, and with older versions of Windows, sometimes impossible. See "Transferring Existing Windows Installations to RAID" on the next page for instructions.

Windows Software RAID: Starting with Windows XP, Microsoft integrated RAID functionality into its operating systems. What type depends on the flavor of Windows:

Windows XP allows spanned volumes (one volume over two or more disks), aka JBOD.
Windows Vista Ultimate allows JBOD and RAID 1 striping.
Windows 7 Home allows JBOD and RAID 1 while Professional and Ultimate add RAID 0 mirroring. Windows 2000 Professional also has

JBOD, 0, and 1. Windows Server operating systems from 2000 on have JBOD, 0, 1, plus support for RAID 5 distributed parity.

Windows RAID offers several advantages. You can create arrays from within Window Drive manager so there's no BIOS to configure. It's also more flexible with mirrors, allowing you to create them from existing volumes containing data, as well as delete either half of a mirror with the other remaining intact. You can mirror individual partitions, including partitions from different drives onto a single drive.

The disadvantages are that other operating systems, such as the Linux used on repair discs, can't see Windows software RAID partitions which use Microsoft's dynamic disk technology. Also, maintenance performed by Windows when it feels it's needed, which can occur any time there's a configuration change, hurts performance while in progress. Restoring mirrors isn't as dead simple as it is with a hardware solution either.

Though you'll see a lot of talk about hardware RAID being faster, this discussion predates modern CPUs which can easily handle the overhead. Windows RAID is actually quite fast.

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+1 for a solution in Windows –  neolace May 23 '12 at 18:00

OK, this is just an idea, I have not tried it.

You might be able to create a new software RAID1 volume with mdadm, like:

mdadm --create  /dev/md0 --level=1 --raid-devices=1 --force /dev/sdb1

You would want to create the volume on the empty disk.

Then you would copy your data onto that RAID volume. Once that is done you could add the disk to the RAID volume.

mdadm --add /dev/md0 /dev/sda
mdadm --grow /dev/md0 --raid-devices=2

Once the RAID is refreshed, you'd have your data on a new volume.

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Reference. –  Diogo May 23 '12 at 17:56
He may need an --assume-clean when creating the initial array. –  Zoredache May 23 '12 at 17:57
+1 for a possible solution in Linux –  neolace May 23 '12 at 17:58
Some recent versions of mdadm default to metadata format 1.2 ( which goes at the start of the partition ), which will cause this to corrupt the existing partition. You will need to use 1.0, which places the metadata at the end of the partition. This can still corrupt the existing partition if it actually uses the last bit of the partition, but sometimes it doesn't. You will certainly want to fsck /dev/md0 first thing. –  psusi May 23 '12 at 19:46

With Software RAID, or Windows Software RAID you can mirror an existing volume, fairly easily. PROTIP, if you don't already have a backup in place, then don't try this, messing around with partitions/filesystems without a backup of important data is just plain stupid.

I have had a hardware RAID controllers that allow you to build a new RAID1 and select which drive will be the master and will be used to initialize the other.

From what I have seen, the vast majority of the sata fakeraid crap you will see built into most motherboards these days do not support this, and will wipe both drives when creating a new volume. But IMO, most of the fakeraid crap is pretty pointless anyway.

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