RAID 6 vs RAID 5 - The Case For RAID 6

RAID-5 is the most popular choice for storage arrays today, as it is relatively simple to implement at the hardware level and is able to continue to operate in the event of failure of a single device. For many years RAID-5 has provided adequate levels of protection for highly reliable operation, but the growth in data storage requirements and the corresponding increase in capacity of arrays has the potential to impact the reliability of RAID-5 systems.

It is easy to see that larger data storage requirements leads to arrays with more drives and with more drives comes a higher probability of one drive failing. However, another problem is now becoming apparent - the rate at which an otherwise healthy occasionally drive fails to read a sector from the disk. These errors are known as "non-recoverable read errors" and the rate at which they occur is typically specified by the drive manufacturer as "non- recoverable read errors per bits read". This rate ranges from one error per 10^14 bits (12.5 TB) read for consumer SATA drives such as the Seagate Cheetah NS.

In order to rebuild the array after a drive failure, a RAID-5 array must read the entire contents of every remaining disk in the array. If the array consists of seven 1 TB disks, 6 TB of data would be read during this process, 1 TB from each of the six non-failed disks. If consumer SATA disks are used, one read in every 12.5 TB of data read is likely to fail, so there is almost a 50% chance of an unrecoverable read error during this process. When such an error occurs the RAID controller cannot continue the recovery process and the array will fail. When this happens, all is not lost. Our experienced data recovery experts can rebuild arrays which have failed in this way, often with same-day turnaround. Call us on 0800 999 3282 to discuss how we can get you back in business as quickly as possible.

RAID-6 improves on the reliability of RAID-5 by being able to tolerate failures on two disks simultaneously, thus considerably enhancing the reliability of the array. This enhanced reliability comes at the cost of additional hardware in the form of the additional disk per array, as well as increased complexity in the RAID controller.

In an ideal implementation, RAID-6 is only marginally slower than a RAID-5 array with the same capacity and identical drives. The minor performance penalty comes from the need to wait for data on one additional disk to rotate to the read heads. The complexity of the calculations required when writing data mean that real world implementations are often far from ideal and are limited in performance by the rate at which parity can be calculated, rather than the speed of the disks.

How RAID-6 works

While a RAID-5 array contains one additional drive, over and above those required to store the data, a RAID-6 array contains two additional drives. The capacity of an array consisting of N drives with minimum capacity C is thus given by the formula (N - 2) * C. For example, a RAID-6 array of seven 1 TB drives would have a usable storage capacity of 5 TB.

The following diagram illustrates how the data and parity blocks are distributed across disks in a RAID-6 system.

RAID 6

A Firmware Affair (RAID 0 Case Study)

Firmware issues

Sometimes it is very difficult to correctly diagnose a drive: the symptoms one is facing can be confusing and can lead you in the wrong direction.

We received a RAID 0 system, made up of 2 drives. One of them was completely unresponsive, it had no sign of life when powered on.

In such situations, the first issue that comes to mind is a major PCB failure; so you have two solutions: replace it with a matching PCB that you know works, or try to repair the damaged board.

Well, this time the PCB swap didn’t help at all.

We checked all the other components and they were fine; at the end of a long process we found that the problem was in the ROM chip: the firmware had suffered a severe corruption.

The word Firmware is related to a collection of small programs, this is what “controls" the hardware to put it simply. Usually, such microprograms are stored mainly on a Read Only Memory chip and partly on the platters.

Nowadays almost all modern intelligent devices have a firmware onboard that oversees the proper functioning of the device.

Maybe you have experienced it with your digital camera or mobile phone: A Firmware upgrade results in a totally new behaviour (hopefully better) of your device.

Well, in our drives case, the FW damages prevented the PCB working at all.
Here come the real issues. Every Hard disk firmware stores some unique information, belonging to that specific drive, vital to its correct functioning: you cannot simply take a FW from another drive and overwrite it.

So, we started a real handcraft job trying to reconstruct the damaged FW modules cutting and sewing from other drives.

Our efforts have been rewarded: the customer was very pleased to be able to have his data back in fully working condition!

R3 Data Recovery is real lab that deals with real disasters each an every day. If you have RAID that has failed or any data storage device, we are the people to contact. Call us today on 0800 999 3282 for immediate help and assistance.

How To Identify RAID Devices

Synology RAID storage device

Modern storage devices come in many forms from simple USB devices that can be transported around in your pocket all the way up to network attached devices that sit next to your router or in your office accessible from your network or over the internet.

This is fine until you need data recovery and you are asked the question "is it a single hard drive or RAID device.." obviously this effects the cost of recovery.

Identifying these devices isn’t always straight forward but I hope this goes some way to explain the difference.

First of all there are a handful of vendors that regularly make multidisc RAID backup devices:

Buffalo, LaCie, NetGear and Gstore to name a few;

These devices can be large and have options on the rear of the unit for safe or large storage which is a giveaway that it’s a multidisc RAID device. The unit is heavy and bulky with lights on the front to indicate disc activity also may have the facility to remove the hard drives to upgrade the storage capacity in the future and also hints that it may be RAID.

Remember if all else fails just a simple Google search on the model will bring up the manufactures details and help guide you through some of the questions you may be asked by the data recovery company.

If we know this it can sometimes make the engineers lives easier as some manufacturers will tell you on their websites the parameters fo the model you may have. This could possibly save hours o time trying different parameters and configs and you could have your data back faster than you thought.

R3 Data Recovery is real lab that deals with real disasters each an every day. If you have RAID that has failed or any data storage device, we are the people to contact. Call us today on 0800 999 3282 for immediate help and assistance.