Even though we recover from mechanical hard disks here daily, their workings never cease to amaze us. Think about it for a second. You go to your computer and type in a file name, and it will be retrieved in a matter of seconds—all because of a mini electro-mechanical orchestra taking place behind the scenes.
So, how do the disk heads move to the exact location on the disk platters where your requested file(s) are stored? This process happens thanks to two motors inside your hard disk drive. The first one is the Voice Coil Motor (or VCM). This actuator motor positions the disk heads near the data tracks where the requested files are stored. However, the VCM lacks the granular precision needed to position the heads at the sector level. This is where the second piezo-electric motor comes into play. This is an actuator motor designed for the exact positioning of mechanical objects. For example, if you drove to work this morning, your car probably used a piezo-electric motor in its fuel injection system. If you took the photos over the weekend with a modern DSLR camera, a piezoelectric motor would probably have been used to focus the lens accurately. Or, if you know of anyone who has undergone minimally invasive surgery recently, the surgeon would likely have used an electro-mechanical instrument controlled by, you guessed it, a piezo-electric motor.
The dual-stage actuation provided by the VCM and piezo-electro motors enables the head-disk assembly to move into place safely and accurately read, write, and erase data. Unfortunately, things are not that simple, and the laws of physics always get their way.
The Problem of Internal Vibration
The head-disk assembly is a tiny and relatively light mechanism. It has the formidable job of reading data from metal-oxide coated spinning metal plates (platters) which store your data. These spin at 5200rpm or 7200rpm. As anyone who has stood on a station platform as a high-speed train passes knows – a whoosh of air or turbulence is created. A similar process happens inside hard disk drives as the platters spin. To minimise this air turbulence, most head-disk assemblies are fitted with dampers. These help absorb some of the turbulence effect and vibrations generated by the moving head-disk assembly. Internal chamber turbulence also explains why some Seagate Exos and Western UltraStar high-capacity disks use Helium. (This gas is one-seventh the density of air and greatly reduces turbulence inside a disk).
The Problem of External Vibration
Electromechanical hard disks are designed to cope with minor physical vibrations during their lifetime. This could be from the physical movement of the disk drive or vibration incurred by the thermal expansion of components (e.g thermal asperities on the platter surface). An embedded servo control system typically interleaves servo information with user data to help keep the disk heads on track. Disks will also use ECC algorithms (such as Reed-Solomon or BCH) to identify corrupted bits caused by vibration events and reconstruct original data.
When External Vibration Exceeds the Normal Operating Parameters of the Disk
However, sometimes, the anti-vibration mechanisms inside an electromechanical disk cannot compensate for the effects of external vibration and data read, write or erase operations do not perform optimally, if at all!
Recently, we assisted an artisan cheese maker in the south of Ireland in recovering data from their Seagate Free Agent USB external disk, which stopped working correctly after it was placed near a chilling machine. This disk worked fine for years until one of their employees repositioned it during an office reorganisation. In its new location, it was subject to the vibrations of their chilling machine – positioned not more than 2 metres from the machine and only separated by a thin plasterboard wall. A few weeks later, their computer did not recognise their Seagate Free Agent disk.
Data Recovery from a Seagate FreeAgent external hard disk
In our clean room, we opened it. Inside was a Seagate S-ATA ST3500830AS. We performed diagnostics to find damaged disk heads # 1 and 3. The whole head-disk assembly had to be replaced with an exact-match model. (Fortunately, we had this already in stock.) This new HDA was aligned and torqued. The firmware was recalibrated. Then, we performed a byte-for-byte image. We recovered everything for them. This saved the company hours of reconstruction work on ingredient lists, accounts files, contracts, and compliance documentation. Just before we closed for the holidays, we received a tasty selection box of farmhouse cheese blocks!
How can data loss be prevented in vibration-heavy environments?
- Ideally, place the host computer as far away as possible from the vibration source.
- Don’t use mechanical hard disk drives in environments with lots of vibration. Even though some disk manufacturers might make “shock-resistant” claims – they’re just marketing gimmicks. Underneath their rubberised casing – there is still an electro-mechanical disk.
- Instead, use an SSD. These are much more resistant to vibrations. However, even these, when subjected to continual vibration, can suffer weakened solder joints and fail.
- Even better, use an industrial-class SSD. These typically use higher-grade materials with additional underfill and reinforced soldering to prevent IC detachment from the PCB during prolonged vibration. Examples include the Kingston iTemp M.2 2280 or Transcend MTE712A.
Drive Rescue Data Recovery are based in Dublin, Ireland. We specialise in the advanced data recovery of hard disks, SSDs, NAS, SAS and RAID systems. We recover from external disks such as the Seagate FreeAgent (320GB, 500GB, 1TB), Seagate FreeAgent Go, Seagate FreeAgent Theater+ and Seagate FreeAgent Go Flex Desk (1TB, 2TB). Contact us on 01 485 3555 – we’re here to help!