When should I use Quick scan and when Deep scan?

Yopevo

Hey all, so I lost a chunk of files off my external drive a few days ago. I tried a couple recovery tools and got them back, so all good there.
But here’s what I don’t get. Most apps gave me the option between Quick Scan and Deep Scan. I went with Quick first (faster right?) but it found nothing. Then I ran Deep Scan it actually found my stuff.
So my question is what’s even the point of Quick Scan? If Deep Scan works better, why not just use that from the jump? Is there ever a time when Quick Scan is actually useful? what the actual difference between Quick and Deep Scan?
Sorry if it’s a dumb question.

HopeInSleep

Yopevo Don’t think of them as alternatives- they’re kind of doing different things.
A lot of recovery tools these days don’t even ask you to pick between Quick or Deep Scan anymore. They just run both behind the scenes, starting with a quick pass to see what file system metadata is still intact, and if that comes up short, they go “deeper” with Deep scan.

The basic difference is this:

QUICK SCAN relies on file system structures that still exist. It looks for deleted entries in NTFS’s MFT or FAT tables, things that the OS marked as “gone” but hasn’t overwritten yet. If it finds those entries, it can restore the files with full metadata: name, location, timestamps, so on.

DEEP SCAN ignores the file system. It scans the disk sector-by-sector for known file signatures (PDF headers, JPEG markers...) and tries to reconstruct files from raw fragments. It works even if the file system is totally wiped or corrupted (but you lose filenames, folder structures, and sometimes end up with partial or junk files too).

7nationArnie

Pretty much what @HopeInSleep said.
To add one thing though different tools love calling this stuff by different names. What one app calls "Quick Scan" another might label as “Deleted File Recovery” or even just “Basic Scan” . Same goes for Deep Scan you’ll see it called “Signature Scan”, “Raw Scan”, “Content-Aware Scan” or “Carving” depending on the software.
But functionally always the same idea - one mode checks the file system for deleted entries .The other digs through raw data for anything that looks like a file.

As to when you should use one and not the other, it’s basically this:

Quick Scan -> if the file was simply deleted, recently.
Deep Scan -> if the drive was formatted, is showing up as RAW, or if Quick Scan finds nothing. You’ll probably lose the original file names and need to let it scan for a whiile but it’s your best shot when the metadata is toast.

tl;dr: Quick = fast & clean if you're lucky. Deep = slower but goes through the whole disk with a flashlight.

Yopevo

Ah I see, I definitely got it wrong then 😅
Appreciate all the replies.

0neWire

@HopeInSleep Deep Scan is a bit more nuanced than just “looking for raw data with no names”.
Basically, for a lot of recovery tools, Deep Scan can be further split into two methods: File Table-Based Recovery and Signature Recovery .

First one kicks in when the file system was damaged/lost (like after a reformat or when the drive shows up as RAW). Even if the system looks blank to the OS, a lot of the original metadata might still be buried in the file tables.
Some tools can read these tables directly and pull out deleted files WITH filenames, folder structure, timestamps, etc. In this case, Deep Scan is still relying on metadata, just deeper structures that Quick Scan didn’t pick up.

So it’s useful when:

The file system was reinstalled
You quick-formatted the drive
You changed the partition type
The partition got lost, but wasn’t completely overwritten

So Deep Scan doesn’t ALWAYS mean “no filenames”. It depends on how trashed the file system is and what kind of scan the tool is actually doing.

Now Signature Scan (a.k.a. file carving) is the raw mode most people associate with Deep Scan. It works independently of the file system and scans for known binary patterns (file “signatures” like “FF D8 FF” for JPEGs, “25 50 44 46” for PDFs, etc.
It doesn’t care where files used to live or what they were named it just pulls any sequence of bytes that fits a known format. That’s why results show up as file0012.mp4, recovered123.docx, and whatnot.

The downside of file carving method (if it’s not obvious yet) is that the recovery tool you’re using needs to recognize the file type in the first place. If you’re trying to recover something less common, like a proprietary camera RAW file or a specialized format from some industry software, and Quick Scan didn’t pull anything useful from the file table… then Deep Scan won’t find it either if your software doesn’t have THAT specific file type in its signature database.

Yopevo

0neWire Thanks for the detailed breakdown, really helpful!!!
So just to make sure I’ve got this right… If the recovery app I’m using doesn’t list a specific file type like let’s say CDR from CorelDRAW, does that mean it won’t be able to recover those files no matter whether I pick Quick Scan or Deep Scan?

0neWire

Yopevo No. If you’re using Quick Scan, the software doesn’t care what file type it is. Compatibility with formats like .cdr, .psd, .dwg, whatever, that’s irrelevant in this case.

Quick Scan just looks at the file system’s records (like the MFT in NTFS), and IF a deleted file’s entry is still there it can recover it regardless of the file type. Doesn’t matter if the software “knows” .cdr or not. It’s just pulling what the file table says used to exist.

BUT if the file system’s been wiped or too corrupted, and there’s no usable file table info left, then Quick Scan won’t find anything. At that point many tools fall back on Signature Scan. And THAT is when file type support matters. If your recovery tool doesn’t include .cdr in its list of supported formats then yeah you’re out of luck. It won’t recognize or rebuild those files from raw data, because it literally doesn’t know what they look like.

HopeInSleep

Yopevo Just want to add that some data recovery software lets you define your own custom file signatures. R-Studio does for example , a few others too. Not something I’ve ever messed with personally, but the option’s there. It’s basically a way to “teach” the software how to recognize a file type it doesn’t already support, like if you're working with something niche. You usually need a few sample files and maybe a hex editor, so it’s not exactly beginner-friendly… but possible.

roman-demian

Just popping in to clear up one thing that can be a bit misleading in marketing pages and UI labels.
When you see “Deep Scan” in data recovery software, don’t think of it as one specific, universal algorithm. It’s more of an umbrella label for “anything beyond the basic/quick pass.”

Depending on the tool, “Deep Scan” might include:

Deeper file table analysis (old MFT/FAT records, lost partitions, quick-formatted volumes)
Searching for lost/hidden partitions and rebuilding them
Pure signature-based scanning (file carving) where it walks the raw space looking for patterns like FF D8 FF and such.

Developers bundle those pieces together in different ways, and then slap “Deep” on top. So two apps can both say “Deep Scan” and do slightly different things under the hood.

On the signature side, a couple of important gotchas:

It’s totally possible for a random region of some other file (say, the middle of a large photo) to contain the same byte sequence as a “real” header. Less capable tools see that pattern, assume “hey this is a file” carve it out, and you end up with a “recovered” file that never opens. That’s a false positive, and you can easily burn hours trying to fix something that was junk from the start.
Fragmentation is another big limitation. Modern OSes scatter files across the disk in non-contiguous blocks. A signature scan usually finds the start of a file (the header), but the rest of the data might be spread all over the drive. If the tool can’t correctly follow those fragments, you only get the first chunk, or a mashed-up combination of unrelated pieces. That’s why carved files are often truncated or corrupted.

✅ For anyone who’s curious and wants to learn more about how this stuff actually works ‘behind the scenes’ we’ve got a couple of great write-ups over on the blog:

🔗 How Data Recovery Software Works - overview of the core mechanisms behind file recovery, Quick vs Deep scans.
🔗 Signature-Based Data Recovery Explained - this one’s written by our author David and goes deep into how file signatures work, why carving files isn’t always clean, and what tools can (or can’t) do.

Yopevo

roman-demian Thanks for the links!!!

oleksandr-lukashyn

One more thing worth noting about Quick Scan: on internal SSDs, it's common to see previously deleted files appear in the scan results. At first glance, this might look promising - it seems like the files are recoverable. But don’t assume they’re intact without checking the file size and preview.

If the file size is 0 bytes, it’s likely the file metadata was detected (from the file system), but the actual content has already been wiped by the TRIM command. In such cases, neither Quick Scan nor Deep Scan will be able to recover the data - the file is effectively lost. This is a typical limitation when dealing with internal SSD recovery 😥