The document discusses best practices for backing up MongoDB databases. It explains that backups are important for availability and recovery from data loss. There are two main types of backups: one-time snapshots that capture a point-in-time view and incremental backups that capture changes since the last snapshot. The key steps for taking a one-time snapshot of a sharded cluster are to stop the balancer, take snapshots of the config servers and secondaries of each shard, restart the balancer, and copy the snapshots. Important considerations for backups include minimizing downtime and optimizing storage efficiency.

1. On MongoDB Backup
2014.05.02.
葉秉哲
William Yeh

2. Why backup?
 Availability vs. recovery
 Cost is impacted by these decisions…
 How much data can you afford to lose?
 How long can you afford to be off-line?
 Ref: “MongoDB Backups & Disaster Recovery”
http://www.mongodb.com/presentations/webinar-backups-and-disaster-
recovery
2.

3. Tasks
3.
Backup Restore
One-time
snapshot
Incremental

4. Two kinds of backup
 One-time snapshot
 Capture a consistent snapshot at a specific
point in time
Not easy in a distributed zero-downtime
production system.
 Incremental backup
 Capture differences since last one-time
snapshot
Oplog is N/A in MongoDB config servers (to be
discussed later)
4.

5. Cluster architecture in
production
5.

6. How about MMS?
MongoDB Management Service http://mms.mongodb.com
6.

7. $$
7.

8. 8.
Backup Restore
One-time
snapshot
Incremental

9. One-time snapshot steps
1. Stop balancer (mongos + config)
2. Take snapshot of config data
3. For each shard, take snapshot of one
secondary
4. Re-start the balancer
5. Copy snapshots in steps 2 & 3
 Ref: “Backup a Sharded Cluster with Filesystem Snapshots”
http://bit.ly/1hqO1kj
9.

10. 10.10.
1
2
3
4
5
Copy outCopy out
Take
snapshot
Take
snapshot

11. #1#1
Stop BalancerStop Balancer
11.

12. Stop balancer… Why?
 “If MongoDB migrates a chunk during a backup, you can
end with an inconsistent snapshot of your sharded
cluster. Never run a backup while the balancer is
active.”
 Ref: “Disable Balancing During Backups”
http://bit.ly/1rnRMfV
12.

13. #1: Stop balancer
var sleep_time_in_ms = 10000;
sh.setBalancerState(false);
while (sh.getBalancerState()
|| sh.isBalancerRunning()) {
sleep(sleep_time_in_ms);
}
// now the balancer is stopped…
Ref: “Disable Balancing During Backups”
http://bit.ly/1rnRMfV13.

14. #2#2
Snapshot -Snapshot -
config dataconfig data
14.

15. #3#3
Snapshot -Snapshot -
secondarysecondary
of each shardof each shard
15.

16. Snapshot the “dbpath”
 Snapshoting step, almost the same:
 #2: Config server
 #3: Secondary
 … but just one difference:
 “Never use db.fsyncLock() on config
databases.”
 Ref: “Backup a Sharded Cluster with Filesystem Snapshots”
http://bit.ly/1hqO1kj
16.

17. Snapshot approaches
 “True” snapshot
 LVM, ZFS, Btrfs, etc.
 Cloud snapshot (EC2, GCE, etc.)
 “Fake-and-slowwwww” dump
 mongodump
 fsyncLock() + tar + pigz
 Wordnik tool: https://github.com/wordnik/wordnik-oss
17.

18. Considerations for snapshot
 Timing
 “Freeze” time period
 Archive (including compression &
transmission)
 Storage efficiency
 Copy-on-write snapshot is better
18.

19. Snapshot: copy on write
 Ref: “ 磁 配額碟 (Quota) 與進階 案系統管理”檔
http://bit.ly/R67Yrd
19.

20. #4#4
Re-start BalancerRe-start Balancer
20.

21. #4: Re-start balancer
sh.setBalancerState(true);
// now the balancer is re-started…
Ref: “Enable the Balancer”
http://bit.ly/1hfKFl2
21.

22. #5#5
Copy SnapshotCopy Snapshot
22.

23. Considerations for snapshot
 Timing
 “Freeze” time
 Archive (including compression &
transmission)
 Storage efficiency
 Copy-on-write snapshot is better
23.

24. 24.
Backup Restore
One-time
snapshot
Incremental

25. Restore approaches
 “True” snapshot
 LVM, ZFS, Btrfs, etc.
 Cloud snapshot (EC2, GCE, etc.)
 “Fake-and-slowwwww” dump
 mongorestore
 Daemon stop + untar
 Wordnik tool: https://github.com/wordnik/wordnik-oss
25.

26. 26.
Backup Restore
One-time
snapshot
Incremental

27. Oplog
 Ordered list of write operations
27.

28. Oplog tools
 Ready-to-use command line tools
 mongodump + mongorestore
 Wordnik tool: https://github.com/wordnik/wordnik-oss
 Tayra tool:
http://www.jroller.com/DhavalDalal/entry/tayra_an_incremental_
backup_tool
 mongosync:
http://nosqldb.org/topic/5173d275cbce24580a033bd8
 Still many others:
 https://github.com/search?q=mongo+oplog&type=Repositories
28.

29. Oplog in real-life
 Replication lag
 Inspect it in real production environment!
 Oplog is N/A in MongoDB config servers
 … Still need to deal with the balancer
 … Still need to use snapshot techniques
29.

30. Replication lag in real-life
30.

31. References
 MongoDB: The Definitive Guide, 2/e
 MongoDB Manual
 http://docs.mongodb.org/manual/administration/backup/
 MongoDB Backups & Disaster Recovery
 http://www.mongodb.com/presentations/webinar-backups-and-disaster-recovery
 Backup Strategies: Keeping Your Data
Safe
 http://www.mongodb.com/presentations/backup-strategies-keeping-your-data-
safe
 http://www.slideshare.net/fehguy/keeping-mongodb-data-safe
31.