It wasn’t long after the introduction of the PC that computer enthusiasts figured out that if you deleted a file on your hard drive, it could generally still be recovered. This was possible because deleting a file only deleted its index entry while the file itself remained intact and undamaged. Armed with this knowledge, many IT professionals rescued deleted files and won the accolades of their panicked customers in the process. But the rules have changed with the modern SSD or Solid State Drive and in most cases, if a file is deleted from an SSD, the file is deleted forever!
To understand why, it helps to understand a little more about SSDs.
Unlike a hard drive which can simply write over existing data, an SSD must 1st erase existing data before it can write new data. The process of erasing a data block is very slow in comparison to writing or reading a data block, and as a result 1st generation SSDs became considerably slower over time. To address this concern, newer SSDs started preemptively erasing recently freed blocks during their idle time. This process is referred to as garbage collection and is found in all current SSDs.
However, initially SSDs did not understand or communicate with operating systems like Windows, consequently when Windows deleted a file and marked the space as free for re-use, the SSD knew nothing about it. As far as the SSD was concerned, this space was written to and was thus in-use. To overcome this build-up of unknown and thus unavailable space, SSD manufacturers introduced a feature called TRIM. TRIM allows the operating system to communicate and inform the SSD of free data blocks as they become available. The SSD will then add these blocks to its list of blocks to be preemptively erased. Unfortunately in the real world, these blocks are erased and prepared for re-use almost immediately. Consequently, a deleted file is now totally unrecoverable within moments of being deleted.
Even if you do a quick format on an SSD, the data will be gone almost instantaneously and forever! Previously with hard drives, it was still possible to recover the original data files even if you formatted your hard drive. See our Recovering Data After a Format blog post for more information on that topic.
There are exceptions where deleted SSD data can still be recovered. This is usually because the SSD, operating system or storage configuration does not support TRIM. Below are some examples where TRIM is not supported and hence, deleted files may still be recoverable:
- Using an older 1st generation SSD or Solid State Drive
- Running Windows versions before Vista and MAC OSX versions prior to 10.6.8
- Using an SSDs inside an external USB or Firewire enclosures, and most NAS boxes.
- File system has become corrupted and the volume is no longer recognized or accessible.
- SSD formatted with FAT16 or FAT32
- PCI Express SSDs generally do not support TRIM
- Encrypted volumes do not usually support TRIM
- SSD RAID arrays do not typically support TRIM.
Solid Sate Drives are becoming much more common as the prices comes down and their benefits become apparent, but as always, there are tradeoffs, and understanding the implications is always important. If we can help resolve your data loss situation or if you just want a second opinion, please don’t hesitate to contact us at 1-800-MEMOFIX or [email protected].
© 2014, David Foster. All rights reserved.