Be able to diagnose replica set health and act on failures: read rs.status() and rs.conf(), explain election and majority requirements, and know how a new member syncs before voting. The single most important thing is knowing when a replica set can and cannot elect a primary.
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Domain overview
Server Administration on C100DBA covers running, monitoring, and recovering MongoDB deployments: replica set topology and elections, storage engine failures, node addition and sync, and configuration inspection. Questions are scenario-based, asking for the immediate or correct administrative action, the consequence of a given topology, or the command that reveals replica set state and member health.
Exam objectives
Restoring service after a storage engine crash, including mongod startup and recovery options
Replica set elections, voting members, arbiters, and how new members catch up before participating
Consequences of two-node replica sets without an arbiter, including loss of automatic failover
Using rs.status(), rs.conf(), and db.serverStatus() to inspect replica set and server state
Assuming a two-node replica set without an arbiter can still elect a primary after one node fails; it cannot, since a majority is required.
Believing a newly added member can vote immediately; it must complete initial sync and reach a healthy state first.
Treating a storage engine crash as recoverable by simply restarting mongod without checking logs and repair or recovery options.
Click any question to see the full explanation and answer options, or start a focused practice session above.
A DBA needs to automate log rotation on a Linux-based MongoDB server without restarting the mongod process. Which signal or command should be used to ensure the current log file is archived and a new one is started?
2When enabling access control on a production sharded cluster, what is the most secure method for ensuring internal authentication between cluster components such as mongos and mongod instances?
3A developer reports slow queries on a specific collection. You decide to enable the database profiler to capture only queries taking longer than 200ms. Which command configuration achieves this?
4In a dedicated server environment, what is the primary reason an administrator would choose to manually decrease the 'storage.wiredTiger.engineConfig.cacheSizeGB' below the default value?
5Which THREE metrics provided by the 'mongostat' utility are most helpful for identifying a performance bottleneck caused by a high volume of concurrent write operations?
6A security audit requires that sensitive document data contained in query parameters must not be written to the MongoDB system logs. Which server configuration setting should be enabled?
7Refer to the exhibit. An administrator attempts to recover a corrupted standalone mongod instance using the --repair flag. Based on the error log output, what is the most appropriate next step for the administrator?
8A server has multiple network interfaces including a public IP and a private management IP. How should the 'net.bindIp' configuration be managed to follow security best practices?
9During a peak load period, the 'page faults' metric in mongostat increases significantly. What is the most likely administrative cause related to server resources?
10An administrator needs to create a restricted user for a third-party monitoring tool. The user must be able to perform backups and monitor server status but cannot read actual document data. Which TWO built-in roles should be combined?
11A DBA executes 'mongodump --oplog' against a primary node in a replica set. What is the specific purpose of the --oplog flag in this administrative context?
12A database is experiencing high latency. You run 'mongotop 5'. What specific insight does this provide compared to 'mongostat' for server administration?
13Refer to the exhibit. The MongoDB process has crashed due to a storage engine error. What is the most immediate administrative action required to restore service?
14Which configuration file setting is used to specify the network interface and port that a mongod instance listens on?
15When adding a new node to an existing replica set, what is the primary factor that determines how quickly the new member will be able to begin participating in elections?
16An administrator wants to audit all authentication attempts on a MongoDB Enterprise instance. Which feature should be configured to track these events?
17Which command is used to verify the current replica set configuration and the state of all members?
18What is the consequence of having a replica set with only two nodes and no arbiter?
19Refer to the exhibit. What is the implication of setting the priority of n2 to 0?
20Which TWO of the following are valid reasons to use an arbiter in a MongoDB replica set?
21You are monitoring a MongoDB replica set and notice that the replication lag on a secondary is increasing steadily. You suspect that the secondary is unable to keep up with the write load. Which administrative action should you take first to diagnose the issue?
22A MongoDB replica set has three members: a primary and two secondaries. The DBA needs to perform maintenance on the primary node without causing an election that could lead to data loss. The maintenance requires stopping the mongod process for 30 minutes. Which step should the DBA take first to ensure the primary steps down gracefully and a secondary takes over?
23A MongoDB DBA is asked to ensure that the mongod process on a Linux server automatically restarts if it crashes. The server uses systemd. Which command should the DBA run to enable this behavior?
24A DBA is configuring a replica set with three members: one primary and two secondaries. The DBA wants to ensure that a write concern of { w: 'majority' } is acknowledged only after the write has been applied to a majority of voting members and has been written to the on-disk journal on those members. Which write concern should the DBA use?
25A DBA needs to grant a new application service account the ability to read and write data in any database except the admin database on a MongoDB 6.0 replica set. The account should not be able to perform administrative actions such as managing users or shutting down the server. Which built-in role should the DBA assign?
26A MongoDB 6.0 replica set is experiencing performance issues during peak hours. The DBA notices that the primary is spending significant time on disk I/O. The DBA wants to identify which collections are generating the most disk reads and writes. Which administrative command should the DBA use?
Be able to diagnose replica set health and act on failures: read rs.status() and rs.conf(), explain election and majority requirements, and know how a new member syncs before voting. The single most important thing is knowing when a replica set can and cannot elect a primary.
The Courseiva C100DBA question bank contains 26 questions in the Server Administration domain. Click any question to see the full explanation and answer breakdown.
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