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I have system with 3 hard drives.

I have the OS on drive one, and drives two and three are in a RAID 1 configuration

Is it possible change the configuration of Drives 2 and 3 such that I can use the space on both drives while not losing any of the data on the RAID set. If this is possible what is the safest way to accomplish this goal.

Edit: I am using software RAID from linux OS

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Are you on hardware or software RAID? – MikeyB Sep 28 '09 at 23:34
-1 for poorly written question, even though it's probably a valid question. – davr Sep 29 '09 at 0:20
Your question cannot be answered unless we know the exact technology used for the RAID 1 configuration. Many software raids will not allow you to transition a disk from RAID 1 to an individual use gracefully. – kmarsh Sep 29 '09 at 12:04

As RAID1 is simply mirroring, you could just remove one drive and run the array in a degraded state. Format the other drive (not while the array is active just in case you accidentally format both drives - I suggest doing this from a single user boot or by booting from a LiveCD that doesn't scan and automate RAID arrays) and you are good to go. If you ever change your mind, just rebuild the array onto the second (or another) drive and you are back to having a RAID1 array in a healthy state.

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have a look at your /etc/fstab

you might have a setup like this:

/dev/sda1    /boot    ext3
/dev/sda2    /        ext3
/dev/md0     /mydatamountpoint ext3

/dev/md0 is your RAID-device.

Where does is come from?

What are your RAID-devices (physical members)?

# mdadm --misc --detail /dev/md0

Should tell you.

# mdadm --manage --help
Usage: mdadm arraydevice options component devices...
This usage is for managing the component devices within an array.
The --manage option is not needed and is assumed if the first argument
is a device name or a management option.
The first device listed will be taken to be an md array device, and
subsequent devices are (potential) components of that array.

Options that are valid with management mode are:
  --add         -a   : hotadd subsequent devices to the array
  --remove      -r   : remove subsequent devices, which must not be active
  --fail        -f   : mark subsequent devices as faulty
  --set-faulty       : same as --fail
  --run         -R   : start a partially built array
  --stop        -S   : deactivate array, releasing all resources
  --readonly    -o   : mark array as readonly
  --readwrite   -w   : mark array as readwrite

This should help you to do some more steps.

  1. Do a backup of your files
  2. umount /dev/md0
  3. mdadm --manage --stop /dev/md0
  4. now you can access your identical partitions / files and do what you want
  5. check your /etc/mdadm.conf or similar and check for unneeded entries
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