Multi-pass imaging of damaged hard drives

Atola Insight Forensic has a complex imaging functionality, which allows imaging even physically damaged hard drives, avoiding their further deterioration.

Most imagers have a linear imaging process. Whenever such imager encounters a bad sector on a drive, the process slows down drastically. This often causes the drive to freeze. Insight operates using a special imaging algorithm that provides deliberate timeout and block size control. This allows speeding up the imaging of damaged drives while maximizing the amount of successfully retrieved data.

Using small block size pays off when you need to retrieve the maximum data from an unstable drive. This approach also significantly slows down the imaging process. It may also increase the possibility of causing further damage to the media. That's why Insight's multi-pass imaging engine uses large blocks with short timeouts on the first few passes. It schedules reads inside slow areas for later and then uses the smallest block size on the last pass. That is when fewer sectors are left to be read.

This technique helps achieve imaging speeds of 500 MB/sec in good areas of the drive. When approaching bad areas, it is the most gentle way possible to retrieve data. And it allows reaching unbeatable overall speed of disk imaging.

The best part is that Atola Insight Forensic will handle block sizes automatically. And it provides the best possible results in the shortest amount of time. This makes Atola Insight Forensic faster in any job than any other commercially available data recovery or image acquisition tools.

Block sizes and timeouts are adjustable. However, the default settings of the passes are based on our decades-long experience in data recovery market to fit most problematic drives. Therefore, it is advisable to follow them, unless a particular drive requires specific settings.

On the first pass, Insight allows 1-second Timeout per block, and the Max read block size is set to 4096 sectors. The default settings of the first pass allow smooth sequential imaging of all modern hard drives in good condition. But when you need to image a hard drive with bad sectors, these settings make Insight skip any areas that slow down reading: it performs Jump on error by 1,000,000 sectors at a time. These settings ensure imaging data from the healthy areas of the drive at top speed, while forcing Insight to return to the problematic areas during the following passes. Atola Insight Forensic splits such areas into smaller ones and allows more time for reading the data within.

While Max read block size remains the same during the second and the third passes, the Jump on error is set to 20000 sectors and 4096 sectors respectively. Insight will allow slightly longer, 5-second Timeouts for attempted reading of the blocks.

On the fourth pass, both Jump on error and Max read block size are yet again reduced, this time to 256 sectors.

On the fifth pass Insight allocates 60-second Timeouts to read the Maximum block size of 256 with just 1-sector Jump on error. It is the last and the most scrupulous attempt to read the remaining bad areas of the drive.

After the final pass, the Imaging Results report will appear to show the eventual number of errors on the drive and other detailed statistics.

When looking at the settings of the imaging passes, you will see the Reverse direction check boxes. With this function selected, Insight will approach skipped areas of the drive from the other side on any selected pass. This way Insight can get more data from a drive before entering a damaged zone. The system will focus on the damaged zone during the following passes.

Another option in the imaging pass settings worth mentioning is Disable read look-ahead option. Most contemporary hard drives have read look-ahead functionality. It makes the drive sequentially read more blocks than requested by software. In good drives, this functionality helps the drive to operate faster by reading and caching more data. But with bad drives, read look-ahead leads to bad areas being addressed more often. This slows down the process and may lead to a complete freeze of the drive. In such cases, disabling read look-ahead option is advisable.

When dealing with a damaged drive, we strongly recommend using Segmented hashing because this method supports multi-pass imaging and handling of bad sectors, and provides better resiliency against data corruption.

To read about the way Insight handles imaging of freezing damaged drives please follow this link.