An undelete file system refers to software mechanisms, tools, or configurations designed to recover deleted files from a storage device, such as hard drives, SSDs, or flash memory. These systems aim to restore data that users or processes may have deleted intentionally or accidentally. It leverages various recovery techniques, including scanning raw disk sectors and analyzing file system metadata.

Below are the typical methods and tools used in undeleting files across different file systems:

• **File Carving**

   This technique retrieves files by analyzing raw data and identifying known file signatures, even if metadata is missing. It works well on corrupted or overwritten systems but can only recover certain file types.

 *Relevant links:*  
 https://www.sleuthkit.org  
 https://github.com/sleuthkit/sleuthkit  

• **Journal Analysis**

   Some modern file systems, such as [[NTFS]] or [[ext3]], maintain journals. Deleted files can sometimes be recovered by examining the contents of these logs to reconstruct file operations.

 *Relevant links:*  
 https://docs.microsoft.com/en-us/windows-server/storage/refs/refs-overview  
 https://ext4.wiki.kernel.org/index.php/Ext4_Howto

• **Metadata Scanning**

   Tools inspect the file system metadata (like inodes in [[ext4]] or [[FAT]] tables) to locate references to deleted files. If the content sectors aren’t overwritten, the entire file can be recovered.

 *Relevant links:*  
 https://github.com/dkovar/analyzeMFT  
 https://www.cgsecurity.org/wiki/TestDisk  

• **Shadow Copies / Snapshots**

   Some operating systems like [[Windows]] support shadow copies, enabling users to restore files to earlier versions even if they were deleted. Similarly, [[ZFS]] and [[Btrfs]] use snapshots to enable easy file recovery.

 *Relevant links:*  
 https://learn.microsoft.com/en-us/windows-server/storage/file-server/volume-shadow-copy-service  
 https://github.com/openzfs/zfs

• **Recovery from File Slack or Unallocated Space**

   File slack (unused sectors within allocated blocks) or unallocated disk space may still contain remnants of deleted files that can be restored using specialized tools.

 *Relevant links:*  
 https://forensicswiki.xyz/wiki/index.php?title=Unallocated_space  
 https://www.cgsecurity.org/wiki/PhotoRec  

Undelete file systems rely on multiple recovery techniques, such as file carving, journal analysis, metadata scanning, and the use of shadow copies or snapshots. Recovery success depends on factors such as whether the disk sectors were overwritten and the type of file system in use. Understanding these tools and methods provides better control over data recovery strategies.

Fair Use Sources:

• The Borg
• File Systems for Archive Access for Fair Use Preservation, quoting, paraphrasing, excerpting and/or commenting upon
• The Borg

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