Configuration

General settings

Image deletion. If this switch is set, the image file will be deleted following the successful generation of the respective error correction file.

Reading preferences

Adaptive reading locates and processes the readable portions of damaged media more quickly. This strategy is particularly effective when the error correction file made for the respective medium is available. In that case dvdisaster will stop reading as soon as enough information for recovering the medium image has been collected. This may shorten the processing time by as much as 90 percent compared with a full reading attempt.

If no error correction file is specified, adaptive reading stops when no unreadable areas larger than specified by the slider below remain in the image.

Limited reading range. Reading will be limited to the given range of sectors, including the borders: 0-100 will read 101 sectors. These settings are only effective for the current session and will not be saved.

Skipping of read errors/Stop reading... The slider value affects the reading strategies described above. Its main purpose is to save time when reading defective media and to reduce mechanical wear on the drive. A large value (e.g. 1024) provides a quick overview of the amount of media damage, but will usually read too few data for a successful image recovery. Smaller values like 16 or 32 are a good trade-off between time spent for reading and data retrieved for recovering the medium image.

The linear reading strategy will only skip sectors during the first pass, e.g. when starting without an image file or when completing a truncated image. When filling in previously unread sectors of an existing image, no sectors will be skipped.

DAO mode. Media written in "TAO" ("track at once") mode contain two sectors with pseudo read errors at the end. By default these two errors are ignored by dvdisaster and the image is truncated accordingly.

If you are extremely unlucky to have a "DAO" ("disc at once") medium with exactly one or two real read errors at the end, activate this button to have these read errors handled correctly.

Split image. Allows the creation of large images on file systems which are limited to 2GB per file (e.g. FAT from Windows). The image is spread over files "medium00.img", "medium01.img" etc. instead of using a single "medium.img" file when this switch is activated.

An image can be spread over at most 100 files, so it can be as large as 200GB in this mode. Error correction files are still limited to 2GB; this will be fixed in one the next versions.

Access to a split image is slower then in the single file case, so this mode should be avoided if possible.

Filling unreadable sectors. Use this field only to exchange images from dvdisaster with other data recovery software. Enter the byte value which the other program expects as a marker for unreadable sectors. The value 0xb0 (176 decimal) is used in h2cdimage which is published by "c't", a German periodical. Avoid using the value 0, as most media contains regular zero filled sectors.

Drive initialization. If the value is greater than zero, dvdisaster will issue the drive a spinup command and wait for the given time before actually carrying out a reading operation. This avoids downspikes at the start of the reading curve.

Error correction settings

The two presets normal and high provide a redundancy of 14.3% and 33.5%, respectively. They invoke optimized encoders to speed up the error correction file creation.

For the Reed-Solomon code used in dvdisaster the redundancy also gives an approximation of the error correction file size: As an example, when encoding a 4GB image using a 25% redundancy the resulting error correction file will be about 1GB in size.

Specifying the redundancy by percent is also possible. Please note that an error correction file with x% redundancy will be approximately x% of the size of the corresponding image file. The error correction capability depends on the statistical distribution of read errors. Therefore small percentage changes in the redundancy usually do not make a huge difference - only changes of 5 percentage points and more will have a recognizable effect on the error correction.

The last (and most dangerous) way of specifying redundancy is to give the maximum size of the error correction file. In this case dvdisaster will choose a suitable redundancy setting so that the overall size of the error correction file does not exceed the given limit (in mega bytes). Using this method has a severe drawback: When using the same setting for images of vastly different size, more error correction information is allotted to the smaller images and less to the larger ones. This does not make sense from a technical view.

Memory utilization. dvdisaster optimizes access to the error correction file by maintaining its own cache. The preset of 32MB is suitable for most systems.