Recovering data, whether it’s important engineering data for a Hydro Electric company or the family pictures for a young family, is very rewarding on a personal level. Of course there is the enjoyment of helping someone in need. But the real reward for a good data recovery technician comes from the satisfaction of solving problems others can’t.
However, not all data recovery cases are solvable and that’s hard for my techs and our clients to hear. One of the most frustrating data recovery scenarios involves uncorrectable read errors. We see a lot of these cases.
In this typical scenario we receive a small 2.5” laptop hard drive for data recovery. We evaluate the hard drive and deem it functional enough to start creating a sector by sector image. But as we image off the drive it encounters more and more Error Check & Correction or ECC errors; to the point that there is at least one unreadable sector for every 5000 sectors we read. When a disk drive encounters a read error it will attempt to read the same sector at least 10 times. This slows the imaging process to a crawl and as a result it’s not uncommon for the imaging to take months to complete. Besides the time delay, the image is also riddled with unreadable sectors located randomly across the entire data area and in close proximity to each other, making it difficult to find large contiguous blocks of error free data. This means many larger files may be damaged beyond being use-able and often the majority of the good data will be restricted to smaller sized files. Depending on the size of the files the client needs, this may be acceptable or not.
What is most frustrating is the fact that there is little that can be done. These errors are the result of data not being written properly to the drive in the first place. Bad in equals bad out!
It helps to understand where these errors are triggered. When a hard drive reads a sector of data, it also reads a 50 byte ECC code that resides just after the real data. When the data was 1st written to the sector it ran a sophisticated algorithm on the 512 bytes of sector data and this resulted in a unique ECC code which can only be replicated by reading the exact same data. When a sector is read later, the drive attempts to validate the data by running the same algorithm on the data and comparing it to the previously stored ECC code. If the code doesn’t match, the disk drive produces an error code and prevents the transfer of the data. The hard drive will normally attempt to re-read the data up to 10 times as it tries to match the ECC code and this process slows the drive down considerably.
With our hard drive expertise we are able to disable the retries and other housekeeping chores that slow the drive down. But even with these shortcuts, it is not uncommon for hard drives with this problem to take weeks or even 2-3 months to completely read off every readable sector, especially if the drive is 1TB or larger.
We do have the capability to use special read commands to bypass the ECC error checking but the data is usually garbage or at the very least, it can never be trusted 100%. We will do this for a few key sectors of data if the situation warrants it.
So what cause these ECC errors to proliferate? ECC errors can be the result of many different causes.
If a weak head is having problems writing data, ECC errors can often be created. The head appears to be stable when it writes the data and even passes the ECC check initially. But when it attempts to read the same sector later the ECC check fails and the request is aborted.
lf a hard drive is running under extreme heat conditions, for example if a laptop gets extremely hot while you are working from home by the swimming pool, the hard drive which is a mechanical device made of many sorts of metals will expand. Writing data while the drive is in this state may cause problems later when trying to read the drive in a cooled down state as the positioning will affected ever so slightly. This shouldn’t normally cause problems but extremes of operability are always unpredictable.
BUT the number one reason for the proliferation of ECC errors in our opinion is a bad memory chip whether on the hard drive or more likely inside the desktop or laptop.
If your storage device is riddled in read errors, we can help and are usually successful in recovering the majority of a user’s data. Costs for these types of cases are typically in the $400-700 range depending on the severity of the errors and the capacity of your hard drive. Please give us a call today to discuss your data loss situation.