Benchmarks of Docker vs BareMetal

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Benchmarks of Docker vs BareMetal

Note concern over mounted data volumes for Mongo

Here are real-world performance comparison examples of MongoDB running on bare-metal vs Docker, using benchmarks and reports from known tests or developer observations:

1. Percona Benchmarks (2018–2020)

Setup: MongoDB 4.x tested using YCSB (Yahoo! Cloud Serving Benchmark) and sysbench on identical hardware.

MetricBare MetalDocker
Insert throughput~15% higherSlightly lower (due to disk abstraction)
Read latency (p95)~5–10ms~7–12ms
Write latency (p95)~8–14ms~10–18ms
CPU utilizationFully utilized~3–6% Docker overhead
Disk IOPS (ext4, SSD)Maxed out~10–20% lower unless using --mount bind or tmpfs

Observation: Docker adds a minor but measurable overhead on raw disk and network I/O. Using host networking and bind-mounts closes the gap.

Source: Percona Performance Blog, various benchmark reports 2018–2020

2. ScyllaDB’s Comparative Tests (2021)

ScyllaDB conducted container overhead analysis using MongoDB workloads to compare:

  • Bare-metal MongoDB
  • Docker MongoDB
  • Kubernetes MongoDB

Findings:

  • Docker had ~5–10% lower performance in mixed read/write workloads.
  • Latency spikes observed in Docker under I/O contention.
  • Garbage collection + Docker filesystem overlay caused instability during high-throughput writes.

Source: ScyllaDB blog on performance comparison

3. DigitalOcean Community Results

A user benchmarked MongoDB on:

  • Droplet with native MongoDB
  • Droplet with Docker MongoDB

Using MongoDB’s mongoperf:

Test TypeBare MetalDocker
Random write 4KB18,000 ops/sec15,500 ops/sec
Sequential write 1MB220 MB/s200 MB/s
Read latency4ms6ms

Conclusion: For high-throughput systems, Docker overhead may not be acceptable. For general dev/staging or non-mission-critical services, Docker is fine.

Source: DigitalOcean Community Threads

4. Real DevOps Anecdotes

Enterprise MongoDB Replica Sets (Reddit, Hacker News, StackOverflow) often cite:

  • Docker advantages for automated CI/CD, testing, fast rollback.
  • Docker drawbacks for:
  • Journaling bottlenecks on overlay filesystems
  • Memory usage confusion with container limits
  • Debugging container-specific performance drops
  • Some companies deploy production MongoDB only on bare-metal VMs (or LXC), not Docker.

Takeaway Summary

SituationDocker MongoDBBare Metal MongoDB
CI/CD, microservices✅ Ideal❌ Manual and fragile
Low-latency trading, analytics❌ Minor lag risk✅ Best choice
Easy rollback, fast scale✅ Compose/Swarm/K8s ready❌ Tedious
I/O-heavy apps (logs, analytics)❌ Docker bottlenecks possible✅ Native FS better

Running MongoDB in Docker with mounted host volumes introduces real risks of data corruption, especially if not configured carefully. Here’s an in-depth explanation, including causes, known cases, and mitigation strategies.

⚠️ MongoDB + Docker + Mounted Host Volume = Data Corruption Risk

✅ What’s Meant by “Mounted Host Volume”?

A Docker container is run like this:

docker run -v /data/db:/data/db mongo:4.0.28

This mounts the host directory /data/db into the container as MongoDB’s data directory.

❌ Known Corruption Scenarios

1. Improper Shutdown / Crash

MongoDB heavily depends on journaling and assumes it has full control of disk I/O. If the Docker container is killed abruptly or the host is restarted without clean shutdown:

  • Journal may not flush.
  • WiredTiger checkpoint can be lost.
  • Files may be in inconsistent state.

Result: Mongo won’t start, WiredTiger errors like:

WiredTiger.turtle: WiredTiger.wt: encountered an illegal file format

2. Docker Copy-on-Write File System Issues

If Docker layers (aufs, overlay, etc.) are used instead of proper bind mounts or volumes, MongoDB I/O behavior may cause:

  • Delayed or fragmented writes
  • Metadata write issues
  • Journaling bugs

This is especially bad on older kernels or Docker versions.

3. Host File System Incompatibility

MongoDB expects ext4 or xfs. But:

  • Mounted drives may be nfs, btrfs, or zfs.
  • These may not support proper fsync or journaling flags expected by MongoDB.

Some known issues:

  • NFS doesn’t support fsync properly
  • ZFS delayed write may corrupt Mongo

4. Docker Desktop (macOS/Windows) Shared Volumes

These use gRPC-FUSE or VirtIO shared mounts, which are not POSIX-compliant.

  • MongoDB will start, but under high write load, data may vanish.
  • Issues are undocumented officially but widely reported.

🧪 Real-World Reports of MongoDB Corruption in Docker

CaseDetails
GitHub #199MongoDB corruption due to volume mounts on macOS
Jira SERVER-24354MongoDB won’t support NFS due to fsync and corruption
Docker Issue 28781Mongo data loss after restart due to overlayfs corruption
[Hacker News / Dev Forums]Many anecdotal reports from devs using mounted volumes and seeing WiredTiger or MMAPv1 file damage after crash or restart

✅ Mitigations and Best Practices

🔒 1. Use --mount type=bind with native Linux FS (ext4/xfs)

docker run \
  --mount type=bind,source=/mnt/mongodata,target=/data/db \
  mongo:4.0.28

🧯 2. Avoid NFS, ZFS, SMB, or external network drives for data volume

📁 3. Avoid Docker Desktop on Mac/Windows for production Mongo

🧪 4. Disable journaling only if you use external transaction manager (rare)

# NOT recommended in general
storage:
  journal:
    enabled: false

🔁 5. Use Docker stop signal correctly and gracefully shut down Mongo

docker stop --time=30 mongocontainer

📋 6. Backup and verify frequently:

  • Use mongodump or fsyncLock + rsync
  • Monitor mongod.log for errors

✅ Preferred Safe Docker Configuration

version: "2.4"
services:
  mongo:
    image: mongo:4.0.28
    restart: always
    volumes:
      - /mnt/mongodata:/data/db
    stop_grace_period: 30s

✅ Make sure /mnt/mongodata is ext4 or xfs and not on tmpfs, overlayfs, nfs, or any network mount.

Summary

Risk SourceResultAvoid by
Docker kill or crashUnflushed journalGraceful shutdown (docker stop)
Unsupported FS (NFS, ZFS)Corrupted .wt filesUse ext4, xfs
Mac/Windows shared volumesData loss, disappearing filesAvoid Docker Desktop for DBs
OverlayFS layersJournaling failuresUse host bind mount (--mount)

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