Moving MongoDB's data folder?

Question

I have 2 computers in different places (so it's impossible to use the same wifi network). One contains about 50GBs of data (MongoDB files) that I want to move to the second one which has much more computation power for analysis. But how can I make MongoDB on the second machine recognize that folder?

Answer 1

When you start mongodprocess you provide an argument to it --dbpath /directory which is how it knows where the data folder is.

All you need to do is:

1. stop the mongod process on the old computer. wait till it exits.
2. copy the entire /data/db directory to the new computer
3. start mongod process on the new computer giving it --dbpath /newdirectory argument.

The mongod on the new machine will use the folder you indicate with --dbpath. There is no need to "recognize" as there is nothing machine specific in that folder, it's just data.

Answer 2

I did this myself recently, and I wanted to provide some extra considerations to be aware of, in case readers (like me) run into issues.

The following information is specific to *nix systems, but it may be applicable with very heavy modification to Windows.

If the source data is in a mongo server that you can still run (preferred)

Look into and make use of mongodump and mongorestore. That is probably safer, and it's the official way to migrate your database.

If you never made a dump and can't anymore

Yes, the data directory can be directly copied; however, you also need to make sure that the mongodb user has complete access to the directory after you copy it.

My steps are as follows. On the machine you want to transfer an old database to:

• Edit /etc/mongod.conf and change the dbPath field to the desired location.
• Use the following script as a reference, or tailor it and run it on your system, at your own risk.
  • I do not guarantee this works on every system --> please verify it manually.
  • I also cannot guarantee it works perfectly in every case.
  • WARNING: will delete everything in the target data directory you specify.
  • I can say, however, that it worked on my system, and that it passes shellcheck.
  • The important part is simply copying over the old database directory, and giving mongodb access to it through chown.

#!/bin/bash

TARGET_DATA_DIRECTORY=/path/to/target/data/directory  # modify this
SOURCE_DATA_DIRECTORY=/path/to/old/data/directory  # modify this too

echo shutting down mongod...
sudo systemctl stop mongod

if test "$TARGET_DATA_DIRECTORY"; then
  echo removing existing data directory...
  sudo rm -rf "$TARGET_DATA_DIRECTORY"
fi

echo copying backed up data directory...
sudo cp -r "$SOURCE_DATA_DIRECTORY" "$TARGET_DATA_DIRECTORY"
sudo chown -R mongodb "$TARGET_DATA_DIRECTORY"

echo starting mongod back up...
sudo systemctl start mongod
sudo systemctl status mongod  # for verification