Case Study: Data Recovery from RAID 5EE System
Case Study: Data Recovery from RAID 5EE System
1. What is RAID?
RAID is an acronym first defined by David A. Patterson, Garth A. Gibson and Randy Katz at the University of California, Berkeley in 1987 to describe a Redundant Array of Inexpensive Disks, a technology that allowed computer users to achieve high levels of storage reliability from low-cost and less reliable PC-class disk-drive components, via the technique of arranging the devices into arrays for redundancy.
More recently, marketers representing industry RAID manufacturers have revised the term to Redundant Array of Independent Disks, a convenient means of avoiding the negative connotations associated with "inexpensive".
"RAID" is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple hard disk drives. RAID's various designs all involve two key design goals: increased data reliability or increased input/output performance. When multiple physical disks are set up to use RAID technology, they are said to be in a RAID array. This array distributes data across multiple disks, but the array is seen by the computer user and operating system as one single disk. RAID can be set up to serve several different purposes. Data can be distributed across a RAID "array" using either hardware, software or a combination of the two. Hardware RAID is usually achieved either on-board on some server class motherboards or via an add-on card, using an ISA/PCI slot.
2. Different Types of RAID
RAID 0 - Striped Disk Array without Fault Tolerance
Provides improved performance and additional storage but no fault tolerance. Any disk failure destroys the array, which becomes more likely with more disks in the array. A single disk failure destroys the entire array because when data is written to a RAID 0 drives, the data is broken into fragments. The number of fragments is dictated by the number of disks in the array. The fragments are written to their respective disks simultaneously on the same sector. This allows smaller sections of the entire chunk of data to be read off the drive in parallel, giving this type of arrangement huge bandwidth. RAID 0 does not implement error checking so any error is unrecoverable. More disks in the array mean higher bandwidth, but greater risk of data loss.
Disk 1 Disk 2 Disk 3 Disk 4
Block 1 Block 2 Block 3 Block 4
Block 5 Block 6 Block 7 Block 8
Block 9 Block 10 Block 11 Block 12
Block 13 Block 14 Block 15 Block 16
RAID 0
RAID 1- Mirroring and Duplexing
Provides fault tolerance from disk errors and failure of all but one of the drives. Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing. Array continues to operate so long as at least one drive is functioning. Using RAID 1 with a separate controller for each disk is sometimes called Duplexing. RAID 1 provides the best performance and the best fault-tolerance in a multi-user system but with an only 50% utilization of the disks.
Disk 1 Disk 2
Block 1 Block 1
Block 2 Block 2
Block 3 Block 3
Block 4 Block 4
RAID 1
RAID 5- Block Interleaved Distributed Parity
Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive. A single drive failure in the set will result in reduced performance of the entire set until the failed drive has been replaced and rebuilt. Raid 5 needs at least three disks and it is one of the most popular implementations of RAID.
Disk 1 Disk 2 Disk 3 Disk 4
Block 1 Block 2 Block 3 Parity
Block 5 Block 6 Parity Block 4
Block 9 Parity Block 8 Block 7
Parity Block 12 Block 11 Block 10
RAID 5
RAID 5E - RAID 5 Enhanced
RAID 5E is a RAID 5 array with a hot spare drive that is actively used in the array operations. In a traditional RAID 5 configuration with a hot spare, the hot spare drive sits next to the array waiting for a drive to fail, at which point the hot spare is made available and the array rebuilds the data set with the new hardware.
Disk 1 Disk 2 Disk 3 Disk 4
Block 1 Block 2 Block 3 Parity
Block 5 Block 6 Parity Block 4
Block 9 Parity Block 8 Block 7
Parity Block 12 Block 11 Block 10
.
. .
. .
. .
.
Hot Space Hot Space Hot Space Hot Space
RAID 5E
RAID 5EE - RAID 5E Enhanced
RAID 5EE is very similar to RAID 5E with one key difference -- the hot spare's capacity is integrated into the stripe set. In contrast, under RAID 5E, all of the empty space is housed at the end of the array. As a result of interleaving empty space throughout the array, RAID 5EE enjoys a faster rebuild time than is possible under RAID 5E.
Disk 1 Disk 2 Disk 3 Disk 4
Space Block 1 Block 2 Parity
Block 3 Block 4 Parity Hot Space
Block 6 Parity Hot Space Block 5
Parity Hot Space Block 7 Block 8
RAID 5EE
3. Routine procedure of RAID recovery via Manual Mode:
Data Compass RAID utility supports data recovery from RAID systems manufactured by IBM (ADAPTECT), HP/COMPAQ, AMI, etc. as well as DYNAMIC HDDs; supported RAID types include RAID 0, RAID 1, RAID 5, RAID 5E and RAID 5EE. Here we are using RAID 5EE system to introduce the newly added RAID Recovery utility of Data Compass. This is an IBM (ADAPTEC) RAID system, composing with 4 segment HDDs, among them, there are only 3 segment disks left, 1 segment disk is lost.
By using the RAID utility of Data Compass kit, users are provided two different ways for importing/ loading the segment disks of the patient RAID system to Data Compass system: one is to connect the physical segment disks to the computer via standard ports or an array card, and import the physical segment disks for analysis directly; the other one, in case users do not have sufficient ports or cards for connecting the segment disks to, is to create an image for each segment disks and then import the disk image for analysis. Please note that the segment disks do not need to be connected to the Data Compass hardware controller, but still you need to connect the hardware controller to the computer before you can launch the program.
Tips: Please disable the “Read Permit” directly on the controller before running the program, otherwise the program may show you “No DC Device Found” and we have to wait until the hardware controller was detected by the computer.
In case the Data Compass was upgraded from Standard to Premium through our free upgrade project, users need to activate the RAID add-on on the first time using the utility. Users should visit us at http://code.xlysoft.net/validen.aspx and register your Data Compass online as “Data-Compass-Premium” using the old Product Number, and then (it takes minutes to hours due to the global time difference) you will receive a license ".key" file sent from the registration system to your registered Email (same like the previous registration). On receipt of the new license key, users can activate the RAID add-on following the instructions below:
Launch DCEXP and select “Activate RAID Add-On” option
Select the License Key for Data Compass Premium, click “Open”
Please note: if the selected license is wrong or invalid, the program will report an error message; users need to exit and launch the program again for activation.
Error Message
After finishing the activation, users are able to use RAID recovery utility to open a RAID system for analysis, see below:
RAID Utility was successfully activated
Data Compass RAID utility supports both “automatic mode” and “manual mode” of analysis.
First, we will introduce how to analyze a RAID 5EE system in automatic mode:
Select Analysis Mode
First select the analyzing mode; then we only need to define the Number of Segment Disks (the original number of disks in the RAID system), RAID Type and RAID Manufacturer. In this example, we have 4 segment disks, RAID type is RAID 5EE and from MANUFACTURER_Standard
Please Note: the IBM RAID controller is SNIA Compatible; all manufacturers belong to MANUFACTURER_Standard, aside from AMI, HP/COMPAQ and DYNAMIC Disk.
The next step is to import RAID segment disks, they can be disk image or physical disk; in automatic mode, users can import the segment disks by random sequence, the program will work out the actual order.
Import Segment Disks
Click “Apply’’ after importing all the segment disks, then program will analyze segment disk sequence and the storage method according to these setting information, and return with all parameters.
Analysis Finishes
Remark: How to understand the returned HDD sequence
HD0, HD1, HD2 and HD3 on the left side represents the importing sequence of the segment disks (this sequence means nothing indeed); 3.1.2.0 on the right side represents the native sequence of the segment disks. For example, the native segment sequence in this case study is 3.1.2.0, which means the segment you imported as HD3 is actually the first segment disk in the RAID system, HD1 is the 2rd, HD2 the 3rd and HD0 the 4th.
By clicking the OK button next to the “Apply” and “Stop” button, program will try to open the virtually created RAID system and display the partitions and files in the DCEXP interface.
Partition of the RAID system shows up in DCEXP
Double click the needed partition, and double click ROOT to show folders and files.
Now users can recover the needed files just like recovering data from a normal HDD.
Second, we will introduce how to analyze a RAID 5EE system in manual mode:
When select Manual Setting, all the parameters should be set manually and you need to know the native sequence of the segment disks (in case you don’t know, work it out by trial and error) and other parameters marked in red frame. In this case, the Number of Segment Disks should be 4, with RAID Type 5EE. Manufacturer Standard, Block Order is RIGHT_ASYNCHRONOUS and Stripe Size is 8KB.
Attention:
1. The IBM RAID controller is SNIA Compatible; all manufacturers belong to MANUFACTURER_Standard, aside from AMI, HP/COMPAQ and DYNAMIC Disk.
2. Delay is only available in HP/COMPAQ RAID system; users don’t need to set this option for RAID system of other manufactures.
3. For all the RAID system of HP/COMPAQ and some of other manufactures, users need to set Header Size for analysis. The Header Size need to match different RAID system and
users normally set it by trial and error according to experience. In this case we don’t need to set the header size, because there is no Header Size (offset) in this RAID system.
After that, import the segment disks exactly in the native sequence. In this case, the third segment drive was lost.
After setting, click “Apply” button and wait until you receive the below message:
By clicking the OK button next to the “Apply” and “Stop” button, program will try to open the virtually created RAID system and display the partitions and files in the DCEXP interface.
Attention: If the parameter set is incorrect and program can’t acquire the partition, users need to reset the parameter and try again *(Manual Mode is a process of trial and error).
Double click the needed partition, and double click ROOT to show folders and files.
Now users can recover the needed files just like recovering data from a normal HDD.
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