For conventional hard disks (HDDs), the smallest unit of storage is called a sector. This traditionally has been 512 bytes with most hard disks of the last 10 years or so using 4096-byte sectors (Advanced Format). Each sector will hold the user-generated data, sync bytes but will also hold some ECC (Error Correction Code) to maintain the integrity of the data. The ECC acts as a sort of checksum to filter out corrupt data before it’s transmitted to the host’s RAM.
The problem with ECC
Modern ECC algorithms (such as Reed-Solomon and Bose-Chaudhuri-Hocquenghem) are great, they help prevent bit-rot and other corrupting processes. However, when you have a failing hard disk with bad sectors and try to read it on a standard PC, ECC will probably be the reason that the disk can’t be read. The host computer attempts to read the sectors once but ECC will report the sectors as unreadable. To the user, they will probably see a “not responding error” or similar on their GUI. ECC is a fusspot in this regard – any corruption at all and it won’t let the host PC read the data.
ECC and consumer-grade data recovery software
ECC is not only problematic for reading failing disks via an operating system, but it is also one of the main reasons why so many consumer-grade data recovery software applications can’t recover data. Like with operating systems, data recovery applications cannot always read from sectors whose ECC is reporting errors. In order to bypass this, these applications will read and re-read inaccessible sectors multiple times in the hope that ECC might allow a successful read. However, for a hard disk that is failing or damaged, these repeated attempts of reading are the equivalent of torture for your disk.
It’s not only ECC…
ATA controllers, as used in standard PCs, require that data transfers from disk to host use the host’s RAM. This can be problematic, especially when processing disks with bad sectors or read-media issues as BSOD events are likely. In addition to this, ATA controllers in standard PCs cannot perform disk re-set operations.
How professional data recovery equipment circumvents ECC errors and the problems associated with standard ATA disk controllers…
- Data recovery technicians use dedicated hardware systems that enable disk-reads that bypass the BIOS and the operating system. They use systems which can ignore ECC errors.
- Moreover, technicians use equipment which can directly read the disk’s error register. This gives the technician (and equipment) much more specific information about the underlying problem. For example, this could be a UNC (un-correctable) data error or a TONF (track not found) error. When the equipment knows what the underlying fault is, it can choose a recovery algorithm to maximise the probability of a successful recovery.
- Data recovery technicians will typically use systems with ATA disk controllers equipped with Ultra Direct Memory Access. This enables direct data transfers whilst bypassing the host’s RAM.
- ATA controllers used in standard computers cannot perform disk re-set operations if the disk becomes unresponsive. A disk re-set operation is much less stressful on a failing hard disk compared to a re-power operation.
Only last week, we were dealing with a very frustrated end-user who was trying to extract data off his LaCie Rugged Thunderbolt USB 3.0 2TB external hard drive. Everything time he connected the disk via a Thunderbolt port to his MacOS system, it would freeze. He found this very frustrating. He had thousands of Adobe PhotoShop (PSD) and Adobe Premiere Pro (PRPROJ) which he needed to transfer to another working disk. Our diagnostics revealed that the disk inside (Seagate Barracuda 2TB ST2000LM015) had developed extensive bad sectors. Using our ECC-bypassing and UDMA-enabled data recovery systems, we were able to transfer his data to his second disk within 48 hours.
Drive Rescue (Dublin, Ireland) offers a complete data recovery service for LaCie Rugged disks. We regularly recover from models such as LaCie Rugged Mini, LaCie Rugged USB-C, LaCie Rugged 3TB LaCie Rugged 4TB, LaCie Rugged 5Tb which are not mounting or not recognised in Mac. Likewise, we recover from LaCie external disks which are showing up in Windows (10 or 11) or from LaCie disks which are making a clicking or buzzing noise.