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How to Recover RAID 5 Data – The Gillware Method

How to Recover RAID 5 Data

RAID 5 is a popular RAID level, seeing use in servers for businesses of all shapes and sizes. While RAID 5 is resilient, it is not immune to failure, and a RAID 5 failure can be devastating. Loss of data, loss of revenue, and loss of customer confidence can set you back days, weeks, or even months. The consequences of RAID 5 data loss can wreak havoc on your business—if you don’t start looking for data recovery solutions on the double. The RAID recovery experts here at Gillware know how to recover RAID 5 data better than anyone else.

Because RAID 5 has single-drive fault tolerance, a RAID 5 array won’t crash, even after one hard drive has failed. However, when a second hard drive fails, the RAID array, and your data, becomes inaccessible. There are dozens of ways a RAID 5 server can fail. A fire, a flood, or a power surge or outage due to a lightning strike can do the trick. Acts of God notwithstanding, these arrays can also fail due to old age as the hard drives inside wear our. And, of course, you can’t rule out human error.

Gillware Data Recovery has a simple, step-by-step method to recover RAID 5 data after a server crash. With our nine-step process, our RAID recovery experts have saved thousands of clients from their failed RAID 5 servers over our past decade-plus of data recovery work. Our data recovery process is 100% financially risk-free, with free inbound shipping and free evaluations. We don’t charge our clients for our work until we successfully meet their data recovery goals.

How to Recover RAID 5 Data – The Gillware Method

QNAP NAS RecoveryStep One: Make write-protected (read-only) disk clones of each of the healthy hard drives in the array.

Gillware’s first step to recover RAID 5 data is to take each of the healthy hard drives in the failed array and create write-protected disk images of them. Our disk image is a 100% identical copy of the original drive, down to the last bit. By using write-blocking tools, we ensure that we’ve created the most exact replica possible and can’t alter any of the data (on either the original drive, or its clone).

Step Two: Diagnose any broken drives, make the necessary repairs, and create as complete disk images of them as possible.

The failed RAID 5 arrays we receive in our lab tend to have two or more failed hard drives. We need to image the broken hard drives, too. But before we can do that, we must fix them first. We make the necessary repairs in our Madison, Wisconsin-based data recovery lab, which features ISO 5 Class 100 cleanroom workstations and an ample library of replacement hard drive parts.

After repairing the drives, we make disk images of them as well as the healthy drives. Sometimes, if a hard drive’s hard disk platters have become scratched or scored, a 100% complete disk image isn’t possible. This is due to the destruction of physical sectors on the disks, which we cannot reverse.

Step Three: By analyzing the RAID metadata on each drive, determine which drive (if any) is stale and should be excluded.

RAID 5 uses special parity functions to reconstruct lost data if one drive fails, but cannot handle two drive failures. After one hard drive fails, the rest of the array functions normally. But as time passes, the data trapped on the failed drive becomes increasingly out-of-date. Sometimes, two or more hard drives fail almost instantaneously. But in most RAID 5 recovery cases, one of the failed drives has become stale.

Every hard drive in a RAID array has metadata placed on it to help determine its role in the array. The metadata, among other things, can tell us the last time data was written to a given drive in the array, helping us determine which failed hard drive is stale. Out of two failed hard drives in a RAID 5 array, we only need one to “fill in” the holes in the array. We avoid using the stale drive to fill in these holes whenever possible. But in some situations, in order to recover RAID 5 data, our engineers have to rebuild the RAID 5 array with the stale drive and salvage the usable data from the array.

Step Four: Use the metadata on each hard drive to determine the RAID array’s geometry, drive order, parity, rotation, stripe size, and RAID algorithm.

RAID 5 arrays use parity calculations to provide fault tolerance if one hard drive fails. The parity data created by the array spreads out in a particular pattern throughout the drives. In order to reconstruct the failed array, we must understand exactly how this parity data has been spread out. Using the metadata on each drive, our RAID recovery engineers can determine how the array has distributed this data across the drives.

Step Five: Emulate the physical RAID 5 array and find the logical units on the array.

To rebuild the array, our RAID recovery technicians write customized emulation software to string the disk images together. We can then identify how the array’s storage space has been carved up into logical units. Small RAID 5 arrays will often have one logical unit spanning their entire capacity. Larger storage area networks may carve up their storage space into multiple units.

Step Six: Find the filesystem geometry within these logical units.

Many of the RAID 5 arrays we see here at Gillware have suffered physical damage. But we also see RAID arrays that have suffered logical damage as well (and occasionally, both). The filesystem comprises the backbone of your RAID’s logical structure, acting as a roadmap to point you to the locations of your files.

Step Seven: Extract and test sample files to make sure the array has been correctly reassembled.

RAID 5 arrays break all of the data written to them into stripes, distributed across the array’s hard drives. If we don’t put the stripes together in the right order, useful data turns into a Picasso painting (only with less value to the artistic world). By testing large files—large enough to have chunks on every drive in the array—our engineers can make we’ve placed the disk images in the proper order. Since this testing method works best with bitmap image files, our engineers call it “the bitmap method”.

Drobo recovery

Since we opened our doors in 2004, we have helped thousands of clients recover RAID 5 data

Step Eight: If necessary, run a raw scan of the RAID 5 array to pick up any files which may have disappeared due to filesystem damage.

Logical damage to a RAID 5 array can cause damage to the filesystem. This can erase the signposts pointing to some files and make them appear to have vanished. Using advanced data recovery tools of our own design, we can scan through the reconstructed RAID 5 array to pick up any files that the directory structure may have made “homeless”.

Step Nine: Extract all available data from the RAID 5 array.

Our work to recover RAID 5 data ends with the failed RAID 5 array properly reassembled. Finally, our RAID recovery engineers pull off all available data from the array and place it on a healthy external hard drive to return to the client. Our engineers make sure that the client’s most important data is as functional as possible. If necessary, we show our client a list of recovered files to make sure we have successfully met their goals.

Contact our recovery client advisors today or submit a RAID 5 recovery case online:

How to Safely Handle a Crashed RAID 5 Server

When you need someone to recover RAID 5 data for you, now you know where it needs to go. You need to bring it to a professional data recovery lab like Gillware. But what should you do before you get in touch with us?

When your RAID 5 server crashes, the actions you take before you even start thinking about data recovery can have a huge impact on the safety of your data. Gillware has twelve handy tips for safely handling your crashed RAID 5 array:

RAID-5 Failure Tips: How to Keep Data Recovery Possible

Keeping Your Data Safe – Tips to Prevent Your Next RAID 5 Crash

When your RAID 5 array crashes, nobody has a good time. In an ideal world, your RAID 5 server would never crash. Nobody would ever need data recovery services. Gillware (and our competitors) wouldn’t exist. But we don’t live in an ideal world. However, just like you, we’d rather live in a world with less RAID 5 server crashes. The better care you take of your server, the less likely you are to end up needing us to help you recover your RAID 5 data:

RAID-5 Setup Tips: How to Avoid the Data Recovery Lab


Will Ascenzo
Will Ascenzo
Will is the lead blogger, copywriter, and copy editor for Gillware Data Recovery and Forensics, and a staunch advocate against the abuse of innocent semicolons.