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I've got 2 NAS drives that are connected through a router via Ethernet.

If I have a wireless laptop and request a large amount of data to be copied from one NAS drive to the other, does the network traffic go direct from the one drive to the other, going via the wired network, or does the network traffic go via my laptop? That is, from the NAS drive's wired network, to the wireless network and then back to the wired network?

Is this a common cause of bottlenecks when copying a large amount of data? And if so, is there a way to avoid it?

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  • Can I assume you're copying from your laptop and not using any copy / paste tools built into the NAS drives?
    – Dave
    Commented Nov 26, 2012 at 10:28
  • That is correct.
    – Strontium_99
    Commented Nov 26, 2012 at 10:31
  • The fastest/best way is copying directly from one NAS to the other via one or the other, and not using a third machine [laptop] to intermediate between the two, but if that's required, copying via a cli program (robocopy on Windows, rsync for BSD/Linux), versus a GUI program, will always be faster
    – JW0914
    Commented Sep 13, 2023 at 14:49

3 Answers 3

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Connect your laptop to LAN, map NAS drives on your laptop and copy data using Total Commander – because it's much faster than Windows Explorer's copy speed.

Also, some NAS have a built-in FTP server and client. You can start the FTP server on one side and use it on the other side to copy the files between them, without using your laptop.

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  • 2
    If your NASs will let you run rsyncd/rsync (Linux) on them, you can copy data even faster directly between the two NASs - because rsync is usually setup to copy only the parts of files that have changed, not whole files. You can replace the firmware on some NASSs with freenas which will let you do such things and more. (Doing so will probably void any warranty on your NAS.)
    – Joe
    Commented Nov 27, 2012 at 8:26
  • Nice Answer Kaveh!
    – Arash GM
    Commented Mar 19, 2013 at 15:31
  • First part of the answer is wrong, the second part is true.
    – bokan
    Commented Oct 3, 2013 at 7:20
  • 'Total commander is much faster than Windows Explorer copy speed' - Do you have any reference to verify that? I can find videos proving in some cases, one is faster than the other!
    – Dave
    Commented Mar 25, 2014 at 7:07
  • Note that this will cause all data to be sent from the old NAS to the laptop first, then from there to the new device, causing twice as much the traffic as when transferred directly - and probably taking twice as long.
    – not2savvy
    Commented Sep 13, 2023 at 14:47
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Depending on how you perform the copy of the data, if you are using your laptop and Windows Explorer to copy the data from one NAS to the next, perhaps copying the data from one network drive to another, then I believe the data copy does go through your laptop since that is the device working as the device in the middle. You could however perform a direct copy of the data from one NAS to the next. As another user mentioned most NAS devices can use FTP, however if you have the option to use RSYNC, then I would go with that method.

Many NAS devices have some version of Linux running in them and as such they probably can perform an RSYNC directly between the two, thus eliminating your laptop as the bottleneck and you might be able to do a block level backup which will only back the data in the file that has changed instead of the whole file, which will lessen the demands on the network.

Another thing you can do to improve the performance between the two NAS devices is to place both of them on the same switch and if you can Link aggregate the NICs on the NAS devices then that too will help, and better yet if you can have a dedicated switch for the NAS devices to connect to, then have the "NAS switch" connected to the LAN, it will also help reduce the additional traffic that would be on the network between the two NAS's

I hope this was helpful, good luck

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Provided your NAS are linux-based (most if not all are), and you are able to use ssh on your NAS, I recommend to use tar and scp for the fastest possible data transfer.

I had to transfer Time Machine backups from one WD NAS to another. I tried the rsync approach, but transferring 1.4 TB of data with rsync would run for days and was still far from finishing. I think that's due to the fact that Time Machine backups consist of thousands of smaller files. If you have fewer and larger files, rsync might be okay.

For me, a combination of tar and scp worked best. This is how you do it:

  1. Activate ssh on both devices if not available already

  2. ssh into the old device

ssh user@new-device-name
  1. cd to the data folder, for example
cd /shares/TimeMachineBackup
  1. Create a tar archive of the files and directories that you want to transfer. Use nohup, so you can logout and let tar keep running
nohup tar -cvf archive.tar file1 file2 directory1 >tar.log &

Note that I don't use compression, because most files do not compress well, and tar turned out to be significantly faster without compression.

  1. Wait till tar has finished. This can take hours. You can check if it is still running using
ps aux | grep tar

  1. ssh into the new device

  2. Copy the archive over, again using nohup to keep it running

nohup scp user@new-device-name:/shares/TimeMachineBackup/archive.tar /shares/TimeMachineBackup/ >scp.log &
  1. Wait till scp has finished. This again can take hours, depending on the file size. You can check if it is still running using
ps aux | grep scp

or you simply check the file size on the new device using

ls -alh archive.tar
  1. Now unpack the archive, again you might want to use nohup, because it takes a while.
nohup tar -xvf archive.tar >tar.log &
  1. Finished.

You're ready to use the new device.

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