28 Feb 2012
Why settle for less? Here’s the valuable functionality you should look for in a full-featured imaging tool.
| Regular Imaging Tool or Imaging Tool with “Some DR Functions” |
Professional Data Recovery Imaging Tool |
| Goal: To copy data from one drive to another. | Goal: To retrieve data from a bad drive and save it to a good one. |
| Model: The drive is represented as abstract linear data storage (array of sectors). | Model: The drive is represented as a device that has read/write heads, disk platters, problematic areas with different types of media issues, and different types of user data. |
| Issues to be addressed on a degraded/unstable drive | |
| a) Different heads usually have different level of degradation and some heads may even fail while others are still functioning. “Imaging by Selective Heads” | |
| - This issue is not addressed. For example, sectors on different heads are processed by the same hard-coded imaging algorithm. The tool has no information on what head each sector belongs to. | - Each head is diagnosed and different algorithms are configured for heads with different levels of degradation. - Sectors on good heads are imaged first. This approach minimizes the risk of drive failure, and also speeds up the imaging process, because in some cases user data may be retrieved after imaging data on good heads only. - The drive may need to be imaged head by head to avoid the extra load of continuous switching between heads while imaging. |
| b) Problematic areas on different drives (and sometimes even on the same drive) usually have different types of media issues. “Imaging by Type of Media Issues” | |
| - This issue is not addressed. For example, sectors on areas with different types of media issues are processed by the same hard-coded imaging algorithm. The tool doesn’t identify types of media issues, doesn’t provide the user with information on what’s happening behind the scenes, and doesn’t let the user modify an imaging algorithm for different types of media issues. Tools with some DR functions may use different read commands, such as “Read Long”, but they still have the above limitations of control over the imaging process. |
- Preconfigure the drive for lighter operation if it has any read instability issues. For example, disable various background firmware processes, such as SMART subsystem and read look-ahead feature, and turn off bad sector auto-relocation. This preconfiguration is required to minimize the risk of drive failure and to speed up imaging process for drives with certain instabilities. - Problematic areas are identified by the tool (prior to any excessive attempts to retrieve data) and skipped during initial imaging pass to be dealt with on later passes (if necessary). This action is required to minimize the risk of drive failure, and also to speed up the imaging process, because in some cases user data may be retrieved after imaging good areas only. - Information about the status of each read sector is saved to the Sector Map to validate integrity of files when the image is done. - Different imaging algorithms are configured for each pass to process problematic areas with different types of media issues. For example, data from bad sectors is retrieved by different read commands, while areas with more severe degradation/damage are skipped to avoid a drive failure. - The tool identifies the type of media issue, provides the user with all required information in this regard on the fly, and lets the user configure an imaging algorithm to respond to each particular issue of the drive. For example, if the drive stays busy more than a certain period of time, reset/repower it and continue imaging; if sector has a media corruption, process it by different read commands; if a certain number of consecutive sectors have a specific type of error, jump over a certain number of sectors; and other possible scenarios. |
| c) Areas with different types of user data have different importance. “Imaging by Type of Data” | |
| - This issue is not being addressed, that is, sectors with different types of user data processed by the same hard-coded imaging algorithm. The tool has no information on what file each sector belongs to. Tools with some DR functions may have “Imaging Files by Browsing” functionality, but this technique (compared to “Imaging by Type of Data”) is much slower and it has a very high risk of drive failure, because it is imaging sectors in the sequence the file system allocated them and so the drive has to jump to a different area of the disk each time the next file fragment is being imaged. It is also not convenient for the user, since to image files the user has to find/select required files and browse to partitions/directories the files are located in. |
- File system elements, such as boot sectors, file allocation tables, file attributes (such as file names) are processed with the highest priority. Sectors that belong to files the client is looking for are imaged then. All other sectors may be skipped as they don’t have any user data to recover. - Before imaging starts, the user should be able to provide information on what type of data needs to be imaged (recovered), such as type of files or particular directory names. This information is usually taken from the client, meaning that no file search/browsing should be necessary for imaging. - No matter what type of user data each sector contains, the tool uses a drive linear imaging sequence, taking into account all other factors, such as head by head imaging or sequence defined by a type of media issue the sector may have. So, a sequence of sectors to be imaged is not defined by other factors, such as the file system allocation information (this would slow down imaging and increase the risk of a drive failure). - The tool provides the user with on-the-fly information about the data that is currently being imaged; including the filename a currently processed sector belongs to. This helps the user make a decision about the imaging process in on-the-fly, such as skipping files that are not critical, when imaging takes too long. |
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