Data Recovery
DATA RECOVERY BLOG

Bookmark and Share

recover hard disk drive fault
data recovery
raid 5 data recovery

Articles

The following articles were written by Zijian Xie, MSc, BEng
R&D Manager, Data Clinic Ltd, Computer Science Labs

Types of RAID 6

1. P+Q RAID6

Each data stripe of a P+Q double parity RAID6 has a standard RAID5 parity and a ‘Q’ parity which is generated by the Reed-Solomon coding algorithm. It allows up to two drives to fail. The minimum number of disks is 4.

P Q Raid 6
The HP ADG RAID6 is a special type of P+Q RAID6. Within each standard data stripe, there are an integer number of smaller data stripes where the P and Q parities remain on the same disk. This is also called delay parity. Generally speaking, this type of RAID6 has a delay parity value of 16.

2. NetApp Double XOR RAID 6

This is also called RAID-DP and has a similar data structure of RAID4. P and Q parities are generated and stored on the same drives. It allows up to two drive to fail. The minimum number of disks is 4.

double xor raid 6

3. X-Code RAID6

Also called vertical XOR RAID6. The minimum number of disks is 4. It allows up to two drives to fail. Each data stripe group has N (disk number) of data stripes. For example, if it has 5 disks, each data stripe group has 5 rows of data stripes as shown in the figure below.

xcode raid 6

4. ZZS Code RAID6

The minimum physical number of disks of ZZS code RAID6 is 5 and it has to be a prime number (5, 7, 11, 13, 19...). But the ZZS coding algorithm also allows one of the drives contains zeros. In another word, the minimum logical number of disk is 4. In the ZZS coding algorithm, it also defines the calculation unit (one cycle) is equal to (n-1)/2 if there is n physical disks in the RAID6. For the example shown below, it has 7 disks, thus, each cycle has three data stripes.


ZZS code raid 6


5. Park Code RAID6

Park is an engineer of IBM. He designed a new coding algorithm to implement a type of RAID6, supports disk number of 3 to 38. Park code RAID6 is always using three data stripes as a calculation unit.

Park RAID 6

Currently, I don't find any software application support the ZZS and Park RAID6. But, with all the disks intact, the data are still retrievable by customised RAID of R-studio. Leave your comments if you know any other types of RAID6 or solutions.

 

Western Digital MyBook Essential

External hard drive comes with 256 bit hardware based encryption

  • Huge capacity
  • Inbuilt WD Smartware s/w
  • 256 bit inbuilt hardware encryption
  • Password protection

Sounds good !.... Sounds good ?... So what if the drive hardware is damaged and there is no backup.... Is is still possible to recover the data ?... We tested two 320GB MyBook Essential drives to see

Both drives are initialized by factory default setting and user passwords are being used. A hex editor is used to view sectors 0 and 1 from both drives.

Sector 0 is the Master Boot Record.

Sector 1 contains what should be zeros in a conventional hard drive. However both these drives contain data on sector 1. The data is unique and different on both drives (as shown in the table below).


Both drives are initialized by factory default setting and user passwords are being used. A hex editor is used to view sectors 0 and 1 from both drives.

Sector 0 is the Master Boot Record.

Sector 1 contains what should be zeros in a conventional hard drive. However both these drives contain data on sector 1. The data is unique and different on both drives (as shown in the table below).

 

Drive A 0x E6 89 D2 0F D3 62 4C F8 3A 2E 7B B7 6A 7A FC BF

Drive B 0x 3A 73 9F 10 1A 47 97 F2 9A 31 BB E5 CC 8F 97 50
 

Now assume both PCBs are damaged and no longer work...

...A PCB from a compatible donor drive is then sourced

Direct replacement of the PCB will not work. The adaptive ROM content on the donor PCB needs to be recreated by the ROM overlay modules on the platter. This can be achieved by a firmware manipulation tool, which is not introduced here. The reason we use a SATA interface PCB instead of USB interface on a donor drive is because the firmware repair utilities don’t currently support USB interface for firmware manipulation.

Once the ROM is regenerated and the PCB is attached to the failed hard drives, both hard drives are spinning up again and recognized by computer correctly.

A hex editor is used to view the same sectors again after replacing the PCB, sector 0 contains some data, which looks like it has been encrypted, and sector 1 contains zeros. Obviously, the contents are totally different to what they were before the PCB was swapped.

The test demonstrates that the original PCB utilizes an encryption feature where the decryption key is unique to the hard drive. Even when the sectors become accessible through a donor PCB, the user files are still not recoverable without the original PCB being fixed. The patterning data stored at sector 1 and some following sectors (which are normally zeros) are the key parameter to the decryption process.

Currently the decryption algorithm is known only by WD, until someone else is able to disclose it by reverse engineering. Bear in mind that, the patterning data will be unknown without the original PCB working. So, to find out the key parameter, the controller chip and/or the firmware modules have to be looked at.

 


 

June 2011

UK workers take regular risks with data security

May 2011

Co-Op suffers data recovery security breach
Hard disk failure - the signs
New virus offers fake hard disk recovery
Data recovery risk