Upgrade a large mongodb database from 3.6 to 6

Question

I have a mongodb 3.6 database with about 7TB of data, and wish to upgrade this to 6.0. It is a very basic db with no replicas, no sharding, etc. Downtime is not an issue - it can be down for days.

I am wondering how to best go about this. If I simply make a copy of the 3.6 db directory and try to load it on an up-to-date mongo version, this doesn't work as I am getting WiredTiger compatibility issues ("Failed to start up WiredTiger under any compatibility version" etc).

I am assuming that a mongodump of the 3.6 and restore in a 6.0 would work in theory, but with this amount of data I'm guessing the dump + restore would take weeks to run, if it even ever finishes?

Answer 1

ok I figured it out

one can simply update the mongo binaries but doing this via all the intermediate versions; first to 4.0, then 4.2, 4.4, 5.0, and finally 6.0

I did this without any copying or backup of the data, but I guess it would be advisable to do so for data you don't want to lose if something goes wrong.

each step follows standard mongodb major-version upgrade, e.g. running db.adminCommand( { setFeatureCompatibilityVersion: "4.0" } ) when having upgraded from 3.6 to 4.0, and so on

Answer 2

Elaborating on @fso4242's answer:

I'm assuming here that this happened due to an upgrade from Ubuntu 20.04 to 22.04, so everything will be "apt-y".

First remove the already installed 6.0 version: apt remove mongodb-org -y && apt autoremove -y

Then:

• wget -qO - https://www.mongodb.org/static/pgp/server-4.0.asc | sudo apt-key add - and use deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.0 multiverse in /etc/apt/sources.list.d/mongodb.list

• start mongod: /usr/bin/mongod --config /etc/mongodb.conf

  • open the mongo-shell with mongo
  • run db.adminCommand( { setFeatureCompatibilityVersion: "4.0" } )
  • wait for the { ok: 1 }.
  • Ctrl-D out of mongo, Ctrl-C the mongod server.

• repeat above steps for:

  • wget -qO - https://www.mongodb.org/static/pgp/server-4.2.asc | sudo apt-key add - and deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 multiverse
  • wget -qO - https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add - and deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse
    • here apt will complain - you can fix it with: apt --fix-broken install
  • wget -qO - https://www.mongodb.org/static/pgp/server-5.0.asc | sudo apt-key add - and deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/5.0 multiverse
  • and lastly wget -qO - https://www.mongodb.org/static/pgp/server-6.0.asc | sudo apt-key add - and deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu jammy/mongodb-org/6.0 multiverse
    • here the mongo cli is replaced by mongosh