Converting RAID 1 to Single Drive

RAID 1, also known as a mirrored set, would seem to be a perfect way to keep your critical data safe. The concept being that you have redundant drives. Whatever gets written to one drive will get written to the other drive. In other words, the drives are mirrored and look exactly the same. Stands to reason then that if you lose one drive you can use its sibling to continue working and eventually recover your data. Well, not everything stands to reason which is why I get phone calls from clients wondering why they can’t get to their drive after losing either the RAID card, or one of the RAID drives crashes. The following is an explanation of why this happens and an offering on how to fix the problem.

First, if you lose the RAID card in theory you should be able to take either one of the drives in the mirrored set, cable it to a standard IDE port, point the BIOS to that drive if bootable and you should be in business. However many times this is not the case for two main reasons. One, many RAID cards store meta data at the front of the drive, usually the first 128 sectors of the drive are reserved for the RAID card to use. Information like drive state, time of last boot, size and other information that is important to the RAID card is stored there If, however, the RAID card is not the primary hardware interface but instead a standard IDE port then the BIOS has no way of interpreting vendor specific data. In other words the BIOS looks at sector zero in the boot sequence, tries to find a Master Boot Record, then execute any boot it may find. The problem with this drive is that the MBR is 128 sectors down the drive since the meta data is stored in that area. Knowing this, we can trick the BIOS into skipping the meta data and pointing right to the OS boot record.

To do this just use the  raid partition repair freeware that we offer on our website. As always choose the drive you want to work on, in this case, the drive you want to update the MBR position. Once the drive is chosen then click on the button “MBR Scan”. This will look at every sector passing it through our MBR verification filter. If the sector data passes the filter then that sector is added to the “Found Partition List”. The next step is to double click on the Master Boot Record in the list that is 128 Sectors down the drive. The double click will make that partition data the active partition and display the data in the partition sector template.

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You will notice in the template there is a heading ‘Rel Sectors’. This is the total sectors from the partition sector to the OS boot record. Since we have moved the MBR 128 sectors back from the OS boot record we must update the value in that field. Normally that value will be 63, however, no matter what the value is just add 128 to that value and put it in the field. If the drive has more than one partition then you must update all of the ‘Rel Sectors’ fields in order to reflect the new offset.

Once you have finished updating the relative sector offset it is just a matter of pressing the write button. Make sure you have the correct drive highlighted and the data is correct in all of the relative sector fields and write the data. That’s it, you should be able to reboot the drive and the logical drives should mount.

For more info on RAID Data Recovery or for more software, visit the RAID Data Recovery Freeware page.