When you reinstall Windows, swap a disk, or replace a NAS, the first instinct is "copy everything over". 4 TB at 100 MB/s is roughly 11 hours, and a power blip halfway through means starting again.
But if the NAS itself did not move, none of that data needs to move either. What gets reinstalled is your local machine. The NAS is a separate box with its own disks, sitting there the whole time.
This post is the migration walkthrough, plus the three places people reliably shoot themselves in the foot.
First, get the model right
local machine (gets reinstalled) NAS (never moves)
+- system drive C: <- reinstalled +- data disk 1
+- apps and config +- data disk 2
+- mounted drive Z: <- temporary +- ... 4 TB, right where it was
+- WebDAV pointing at the NAS
Reinstalling your OS should not touch NAS data at all. It should only rebuild how you reach that data. A mounted drive is exactly that - the access method. Remount it after the reinstall and everything is still there.
Before you reinstall: mount it, and write down how
Do these two things first, otherwise the worst part is not missing data - it is data that is still there but you cannot remember how you reached it.
1. Mount your important shares as drive letters
Z: -> WebDAV://nas.local:5005/photos
Y: -> WebDAV://nas.local:5005/docs
Separate letters are not cosmetic. One is huge and read-mostly, the other is small files you hit constantly. Mixing them means one access pattern drags the other down.
2. Save the connection details somewhere local
- WebDAV URL and port
- Username and password (many NAS appliances issue a separate app-specific password for third-party clients)
- Mount tuning: chunk size, cache size, timeout
- The NAS hostname or LAN IP
Put this in a plain text file on a USB stick, or in a directory on the NAS you can read without the mount. Do not put it inside a synced folder - it will get overwritten along with everything else.
After the reinstall: five steps
Step 1: install a WebDAV client
The built-in Windows WebClient works, but it has real quirks (stale caches, large directories hanging). ScsDriver is $5.50 lifetime.
Step 2: mount the drive letter
scheme WebDAV
address https://nas.local:5006
username your-user
The drive letter should appear in Explorer.
Step 3: verify before you sync anything
This is the single most important step in the whole migration.
Plenty of people mount, immediately hit sync, and end up pushing the empty folders off the fresh system drive back up to the NAS, overwriting what was there.
What to do instead is verify read-only:
- Open a directory on the NAS you are certain about (say
photos/2023) - Check file counts, sizes, and thumbnails against what you remember
- Confirm the NAS copy is complete, is the older copy, and is unmodified
Do not touch any sync button until this passes.
Step 4: test sync on a small directory
Do not start with 4 TB. Pick a folder of a few hundred MB, run one two-way sync, and watch:
- Is the direction right? Do local edits reach the NAS?
- Do you get conflict files?
- Is the throughput acceptable?
Once the small folder behaves, widen it.
Step 5: full sync
This is usually fast. Most files already exist on the NAS, so the sync tool only transfers the delta - whatever you actually created or changed on the old machine.
The three ways this goes wrong
Failure 1: two-way sync running the wrong way
The new system drive is empty. The NAS is full. If you enable two-way sync before verifying, the tool may decide the extra files on the NAS are meant to be deleted.
Defence: start with one direction (local to NAS), and keep the first run small.
Failure 2: cache makes you see stale data
Mounts cache. If a file changed on another device, the mounted drive may still show you the old version.
Defence: when "I changed it and nothing happened", clear the client cache or remount before blaming the NAS.
Failure 3: the tool treats the mount as a local disk
If your sync tool sees Z: as an ordinary local disk, it will write state files onto the mount and may kick off a pointless full-disk scan.
Defence: configure the NAS side as a network path rather than a drive letter, or tell the tool explicitly that Z: is a virtual drive.
A simpler idea: for a plain reinstall, skip the sync entirely
If you are only reinstalling the OS and the NAS never moved, the sync step is redundant. Remount and read directly.
The only thing that genuinely needs syncing is data you created on the old machine - new downloads, newly organised photos.
So the lean version is:
- Install the client after the reinstall
- Mount the drive letters
- Read directly, no full sync
- One-way sync just your personal folders from the old machine
4 TB of data, zero bytes transferred.
Pricing
| Option | Price |
|---|---|
| ScsDriver | $5.50 lifetime |
| Trial | $0 for 7 days, each invite adds +7 days |
$5.50 lifetime, or $0 for 7 days while the trial promotion runs. If a reinstall is on your list, walk the whole flow during the free week - mount, verify, one-way sync. Get those three moves smooth now and the actual reinstall day will be boring.
Top comments (1)
Nice walkthrough! 😊
I completely agree with the central point: reinstalling Windows shouldn’t mean moving terabytes of data that are already safely stored on a separate NAS. A few small observations from a systems administration perspective, if you don’t mind. For a Windows machine on a local network, I’d generally consider SMB 3.x before WebDAV, unless there’s a specific reason to use WebDAV over HTTPS. I’d also be careful with the initial sync direction. A fresh Windows installation may have empty local directories, and depending on the sync tool’s deletion semantics, even a one-way sync can produce unexpected results. Starting with a read-only verification and a dry run with deletions disabled seems safer. One more thing: I’d avoid storing NAS passwords in plaintext on a USB drive. An encrypted password manager would be a better option.
And perhaps the most important distinction: synchronization isn’t backup. NAS snapshots or versioned backups are still worth having before any migration. I especially liked your final recommendation to skip synchronization entirely when the NAS itself hasn’t changed. Sometimes the best migration is the one that doesn’t move any data at all. 😄
Thanks for sharing!