Restoring a Physical Backup to a Self-built Database

A replica set instance has only one copy of data, while each shard of a sharding cluster has one copy of data. Please restore your data according to your business needs. This document describes how to restore a single copy of data.

Restoring Data to a Single Node

1. Copy the data to an empty data directory in the self-built database, such as /data/27017/.

   cp -r * /data/27017/

2. Restart mongod and check the data. Below is a command sample:

   ./mongod --dbpath /data/27017 --port 27017 --logpath /var/log/mongodb/27017.log --fork

Restoring Data to a Replica Set

As a physical backup retains the configuration of the original instance by default, the original configuration needs to be removed first; otherwise, the data may become inaccessible.

1. Restore the data to a single-node self-built database and then restart the node in the form of replica set. Below is a command sample:

   ./mongod --replSet mymongo --dbpath /data/27017 --port 27017 --logpath /var/log/mongodb/27017.log --fork

2. Log in to the node and remove the replica set configuration of the original instance by running the following command:

   rs.slaveOk()
   use local
   db.system.replset.remove({})

3. Restart the node, add a node to the replica set, initialize it, and check the data. The node added to the replica set should have been started with no data contained. Below is a command sample:

   rs.initiate({"_id":"mymongo","members":[{"_id":0,"host":"127.0.0.1:27017"},{"_id":1, "host":"127.0.0.1:27018"},{"_id":2, "host":"127.0.0.1:27019"}]})

   For more information on the rs.initiate() command, see MongoDB Manual.

Data cannot be restored to a sharding cluster. As the route of physical backup is missing in a sharding cluster, mongos can only read the data of the master shard even if the data of each shard is restored to the self-built replica set (each shard of the sharding cluster).

Restoring a Logical Backup to a Self-built Database

• To avoid any impact on data check after the data is restored to a self-built database, the self-built database must be empty.
• For v3.6, you need to delete the config directory manually and then run the mongorestore command to restore the data of each shard as shown below:
• For v3.2, you need to merge all the files in individual tables manually before restoring the data. Below is a file merge operation sample:
  The c_10 table is in the ycsb directory in the database and contains data files from c_10.bson.gz.chunk-64 to c_10.bson.gz.chunk-127. The merge command is cat c_10.bson.gz.chunk-* > ./c_10.bson.gz.

Run the mongorestore command to restore the data, where the -h parameter specifies the self-built database address, --dir specifies the directory of the data file, and --gzip must be specified to decompress the backup file. The command is as follows:

./mongorestore  --gzip --drop -h127.0.0.1:27017 --dir ./1544517027220146694