SD card recovery software: the free tools and what limits them

Before any software: stop writing to the card

Deleting a file does not usually erase it. Microsoft says: “In the Windows file system, the space used by a deleted file is marked as free space, which means the file data can still exist and be recovered.” The TestDisk documentation says the same of the file systems on cards: FAT is “mainly used on memory cards from digital cameras and on USB keys”, exFAT is found on large memory cards, and when a file is deleted its data area is marked as free. “If the data area hasn’t been overwritten by a new file, the file is recoverable.”

The first rule recurs in the documentation. PhotoRec’s page says that as soon as a picture or file is deleted, you should not save any more pictures or files to that memory device, and Disk Drill’s page says to stop using the card as soon as you suspect data loss. Microsoft gives the equivalent for a computer: “If you want to increase your chances of recovering a file, minimize or avoid using your computer.” The second rule is where the recovered files go: a different drive from the card, which Microsoft makes a requirement and PhotoRec asks you to choose.

Windows File Recovery, Microsoft’s own tool

Microsoft’s page describes a command-line app, installed from the Microsoft Store, with a syntax of source drive, destination drive, a mode and optional switches. Its two basic modes are Regular and Extensive. For an SD card the choice is made for you: the page’s table gives, for FAT and exFAT in any circumstance, Extensive mode, and it says that “Recovering files from non-NTFS file systems is only supported by extensive mode.” Regular mode is for non-corrupted NTFS drives, and Extensive is the thorough option suitable for all file systems; Microsoft notes that it may take a while.

The source and destination drives must be different, and Microsoft creates a recovery folder on the destination for you, named with the date and time. If you have only one drive, it says to use a USB or external hard drive as the destination, and not to create a partition after losing data, “because this reduces the chance of a successful recovery.” You can narrow what is recovered with the /n switch, which takes a file name, a path, a file type or wildcards, and the page gives examples for photos in JPEG and PNG form. Press Ctrl+C to stop the operation.

TestDisk first, then PhotoRec

The two tools come from the same author, and the documentation puts them in order. For FAT and exFAT, TestDisk can read the deleted directory entry and find where the file began, so you select the partition, choose Undelete, select a file and press c to copy it. The same page ends: “If TestDisk has been unable to find your lost data, try PhotoRec instead.” It adds a limit: on ext3 and ext4 the location of the deleted data is no longer available, so TestDisk cannot recover files there.

PhotoRec’s own page calls itself free, open source and multi-platform, distributed under the GNU General Public License, and says it uses read-only access to the drive or memory card. It searches for known file headers, so it can recover a whole file when there is no fragmentation, and it recognises more than 480 file extensions, about 300 file families. You select the disk and partition, choose the file types if you want, choose the whole partition or only the unallocated space (only deleted files, available for FAT12, FAT16, FAT32, NTFS and ext2 to ext4), and choose the directory for the recovered files. They are written to recup_dir.1, recup_dir.2 and so on, and you can open them before the recovery finishes.

On Windows, PhotoRec has to be started from an account in the Administrator group. For Mac SD memory card recovery, which older guides call OS X SD card recovery, the page says to start PhotoRec with the photorec program, and that if you are not root it will restart itself using sudo after a confirmation, asking for your Mac user password. TestDisk’s documentation adds that on macOS the raw device, /dev/rdisk*, gives faster data transfer than /dev/disk* when it is available. We did not run either tool.

When the videos come out unreadable

A whole chapter of the documentation is about this. It says that videos from some digital cameras are fragmented on the card, and “Data recovery software, PhotoRec included, expect non fragmented files.” If every .mov or .mp4 that PhotoRec recovers is unreadable, you are probably in this case; the page says it does not concern copies or downloaded files, only files written by a camera. Sorted by name, the recovered files alternate between _ftyp.mov and _mdat.mov, and joining each pair, with the type command on Windows or cat on macOS and Linux, can rebuild a playable file. The chapter says plainly: “This solution works only for videos written in two fragments.” It names GoPro models whose videos are stored in more than two, which need special software.

What no tool can promise

The tools’ authors write “can” and “if”: the data can still exist, the file is recoverable if the area has not been overwritten. Sellers write more. Remo’s page says its own program showed a “100% success rate even in the most complicated data loss scenarios”, including formatted cards. Disk Drill’s page is more careful on one point: “Recovery may not be possible if a full format is performed.” It adds that the same is true after a camera format that uses the SD_ERASE function, if the card’s controller supports certain commands: “the memory blocks would have been overwritten with zeros.” The pages we read from the tools’ authors do not rank the kinds of format by risk; the warning is about a full format and about SD_ERASE.

The paid and free-to-try programs

The search results are mostly about programs that sellers call SD card data recovery software or SD memory recovery software. Disk Drill’s page advertises free scans and file previews; EnosTech’s comparison table lists Disk Drill with a 100 MB free limit on Windows and a price of $89 a year or $149 for life, Wise Data Recovery with 2 GB free and $44.96 a year, and UFS Explorer with 256 KB per file free and $64.95. HandyRecovery, a site that ranks such programs, shows prices between $64.95 and $89. Recuva’s own page says it recovers files from a Windows computer, the recycle bin, a digital camera card or an MP3 player; it offers a free version, and the Professional version adds virtual hard drive support, automatic updates and priority support. We tested none of these, and Remo and CleverFiles sell the programs they describe.