RAID 6 Data Recovery

While RAID 5 is still one of the most popular RAID levels, many people are turning to RAID 6 for their data storage needs. RAID 5 has its advantages over RAID 6, but the latter offers a stronger safeguard against failure. A RAID 6 array is just like any other storage device, though. It is not immune to failure and data loss. If you’ve lost data due to a RAID 6 array failure, our RAID 6 data recovery experts can help you.

 
 

What Is RAID 6?

RAID 6 is essentially RAID-5 taken a step farther. A RAID 5 array stripes its data across multiple disks and includes parity data in case one disk fails. A RAID 6 array does the same thing. But then it adds more parity data. Due to its second layer of parity, RAID 6 is tolerant of up to two drive failures. It does, however, require one more hard drive than RAID 5 to hold the same amount of data, as the parity data take up twice as much space. Whereas a four-drive RAID 5 array would have three drives’ worth of capacity, a four-drive RAID 6 array only has two.

RAID 5 and RAID 6 both use XOR, or “exclusive or”, logic to provide parity. For parity calculations, XOR logic works on the bit scale. Using the XOR function, all of the bits of one missing hard drive’s data can be reconstructed using the remaining drives. But this only works if one drive is missing. XOR logic can only go so far. Whenever more than one drive is missing, no amount of XOR parity calculations can fill in the rest of the gaps.

In a RAID 5 array with five hard drives, one out of every five blocks contains only parity data. The parity blocks are spread out across the drives to increase efficiency. In a RAID 6 array with the same number of drives, two out of every five blocks contain parity data. The extra parity blocks in a RAID 6 array don’t rely on XOR coding. Instead, they use Reed-Solomon error correction codes.

Reed-Solomon Parity

Reed-Solomon error correction codes were developed by Irving S. Reed and Gustav Solomon in 1960. Since then, Reed-Solomon encoding has become a mainstay in many consumer technologies. CDs, DVDs, and Blu-Ray disks all use Reed-Solomon codes to handle the inevitable burst errors which occur when data is being read. Reed-Solomon encoding is also the reason why a scanner can read a bar code or QR code, even if the code has been partially damaged. Reed-Solomon encoding also sees use in interplanetary data transmissions. While XOR parity relies on simple XOR logic functions, Reed-Solomon encoding relies on Galois field algebra, which is about as complicated as it sounds.

Reed-Solomon encoding in RAID 6 means that a second missing drive can be replaced by the calculations performed on the remaining drives long after the first drive has failed. When one drive is missing, XOR parity calculations on the other drives fill in the gaps. If another drive goes missing, Reed-Solomon parity calculations can recreate its data based on the parity data of the remaining drives (including the parity blocks filling in for the first missing drive).

There are ways in which RAID 6 is less desirable than RAID 5. Because it has to do more parity calculations each time it writes data, RAID 6 is slower than RAID 5. RAID 6 also requires more hard drives to have the same amount of space. But having more fault tolerance to the tune of two drives’ worth of parity data is nothing to sneeze at.

How Can a RAID 6 Array Fail?

Just because a RAID 6 array has more fault tolerance, however, doesn’t make RAID 6 failure impossible. While RAID 6 failure is certainly less likely, no level of RAID array is perfectly insulated against failure. And ironically, the one thing that is meant to prolong a RAID 6 array’s life can also hasten its demise.

When a hard drive inside a RAID 5 or RAID 6 array fails, it can be replaced. The RAID controller takes the fresh drive and begins running its parity checks on the other drives. Using the parity data, the controller turns the new drive into an exact duplicate of the old one. This process is referred to as “rebuilding” the RAID array. A RAID 6 array can be rebuilt if one or two drives have failed. However, there are risks to rebuilding a RAID 6 array.

A RAID 5 or RAID 6 array is in its most vulnerable state when it is being rebuilt. The still-functional drives must pull double duty while the new drive (or drives, in the case that two drives in a RAID 6 array have failed) is being integrated into the array. They are put under much more strain than usual. This can actually cause one or more drives to fail during the rebuild process. Furthermore, the time it takes to rebuild a RAID 6 array depends on the size of the drives in the array. As hard drive capacities increase, rebuild time rises, dramatically increasing a RAID 6 array’s window of vulnerability.

Multiple simultaneous hard drive failures are rare, but can occur. Hard drives can fail under the stress of a RAID rebuild. A sudden power surge or loss of power can cause several drives to crash at once. If the drives in your array came off the assembly line within minutes or days of each other, they could fail within minutes or days of each other too. Natural disasters and freak accidents can cause a RAID 6 crash. And RAID arrays like RAID 6 have no safeguards against data loss due to file deletion or reformatting.

The RAID 6 Data Recovery Procedure

RAID 6 devices may be well-protected, but no data storage device is 100% failure-proof. A RAID 6 array is no replacement for a secure, off-site backup of your data. Fortunately, there’s no need to panic if you’ve lost data due to a RAID 6 crash. Our RAID 6 recovery engineers can help you.

Free RAID 6 Data Recovery Evaluation

Our RAID 6 recovery efforts begin with a free evaluation. We send you a free inbound UPS label to cover shipping costs. After one to two business days, our recovery engineers will have a statement of work for you. This statement of work includes a firm price quote, a probability of success, and an estimated time to completion. We will only move forward with the RAID 6 recovery procedure if you are comfortable with our terms.

Independent Analysis of Your RAID 6 Array’s Hard Drives

Our RAID 6 recovery engineers’ first goal is to create as complete of a forensic image of all the drives in your array as possible. Any necessary repairs to the failed hard drives from your crashed RAID 6 array are made in our ISO-5 certified cleanroom workbenches. Highly trained and skilled engineers in our data recovery lab carry out the repairs. When rebuilding a RAID array, we never work with any of the original drives in the array. Our forensic imaging software is write-blocked, so we never alter any of the information on the original drives.

All of the hard drives in a RAID 6 array have special metadata written to them by the RAID controller. This metadata helps the RAID controller know exactly how the hard drives are arranged. Our RAID 6 recovery experts use this metadata to make sense of the arrangement of the drives in the array. Everything from the order of the drives to the location of the parity blocks and when each drive stopped working can be discerned from this metadata.

If there are any unrecoverable portions of the drives, our RAID 6 recovery experts work around them. Our goal is to provide you with as much functional and uncorrupted data as possible. There is no cost, upfront or otherwise, associated with our RAID 6 recovery process until we recover your critical data. If we are unable to get your important files back, you owe us nothing.

Reuniting You with Your Data

After you pay for our data recovery efforts, we extract your recovered data to a password-protected external hard drive. This hard drive is then shipped to you. You are the only party other than our customer service representatives who know the password. This keeps your data secure in the event of an error occurring during shipping. We hold onto your data for five business days after your scheduled delivery, to give you enough time to make sure nothing has gone wrong. Once that grace period is over, we erase the data from our system. We make certain that you are reunited with your data as safely and securely as possible.

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