Once this block size is known, PhotoRec reads the media block by block (or cluster by cluster). Otherwise, PhotoRec reads the media, sector by sector, searching for the first ten files, from which it calculates the block/cluster size from their locations. If the filesystem is not corrupted, this value can be read from the superblock (ext2/ext3/ext4) or volume boot record (FAT, NTFS). To recover these "lost" files, PhotoRec first tries to find the data block (or cluster) size. This means the data is still present on the filesystem, but only until some or all of it is overwritten by new file data. When a file is deleted, the meta-information about this file (filename, date/time, size, location of the first data block/cluster, etc.) is lost e.g., in an ext3/ext4 filesystem, the names of deleted files are still present, but the location of the first data block is removed. The seek time of mechanical drives is significant for writing and reading data to/from a hard disk, so that is why it is important to keep the fragmentation to a minimum level.
In general, most operating systems try to store the data in a contiguous way so as to minimize data fragmentation. The cluster or block size remains at a constant number of sectors after being initialized during the formatting of the filesystem. Functionality įAT, NTFS, ext2/ ext3/ ext4 file systems store files in data blocks (also called data clusters under Windows). It can be used for data recovery or in a digital forensics context. Recovered files are instead written to the directory from which PhotoRec is run, any other directory may be chosen.
PhotoRec does not attempt to write to the damaged media the user is about to recover from. It is also possible to add custom file signature to detect less known files. It can recover the files with more than 480 file extensions (about 300 file families). PhotoRec is a free and open-source utility software for data recovery with text-based user interface using data carving techniques, designed to recover lost files from various digital camera memory, hard disk and CD-ROM.
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