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I like to optimize my backup strategy of my MongoDB. I have dedicated folders for each database:

storage:
  dbPath: /mongodb
  directoryPerDB: true
  journal:
    enabled: true
  wiredTiger:
    engineConfig:
      directoryForIndexes: true

Gives folders like this:

$ tree -d /mongodb
/mongodb
├── admin
│   ├── collection
│   └── index
├── config
│   ├── collection
│   └── index
├── finaldata
│   ├── collection
│   └── index
├── diagnostic.data
├── temporarydata
│   ├── collection
│   └── index
├── journal
├── local
│   ├── collection
│   └── index
└── _tmp

Folder/database temporarydata contains only temporary data, as the name implies. I like to exclude folder /mongodb/temporarydata from my backup. What happens if this folder is missing from restore, i.e. what happens if this folder is deleted.

Of course, after restore I have to create a fresh and empty temporarydata database with all collections and indexes.

The Mongo Deployment is a Sharded Cluster. Database temporarydata is sharded but all collections in this database are not sharded (I like to distribute the data by using a different Primary Shard, that's the reason why this database has sharding enabled)

Note, I don't like to delete single *.wt files as mentioned in https://serverfault.com/q/911606/463025, the entire database folder would be deleted.

Does it work?

0

I deployed a sharded Cluster on my PC and run a test.

  • Stopping all mongod and mongos services
  • Delete all dbPath at PRIMARY hosts
  • Delete all dbPath at ARBITER hosts
  • Delete folder temporarydata at SECONDARY hosts

Then I would have the situation like I have after a restore from filesystem restore.

  • Start SECONDARY host in standalone maintenance mode
  • Drop temporary database: db.getSiblingDB("temporarydata").dropDatabase()
  • Shutdown the MongoDB
  • Repeat above with all shards
  • Start all mongod and mongos services in your cluster

The cluster started successfully without any error - at least I did not see any. So in principle it seems to work.

However, for testing I deleted also folder+database finaldata. This database is sharded and has sharded collections. After deleting the finaldata folder I was not able anymore to start the SECONDARY mongod service - not even in "standalone maintenance mode". Option --repair does not help either.

Unless I will get a qualified answer on my question I will not got for this backup strategy, it is to risky.

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