What is Ceph?
Ceph is an open-source, software-defined storage platform that is capable of scaling seamlessly, handling failures automatically, and delivering reliable performance across massive clusters.
Core components include:
- RADOS (Reliable Autonomic Distributed Object Store)
- OSD daemons (Object Storage Daemons)
- MONs (Monitors) for cluster quorum
- CRUSH algorithm for data placement
- Librados client libraries
- Gateways and drivers for block (RBD), file (CephFS), and object (RGW S3/Swift-compatible)
Ceph’s architecture separates metadata from data, distributes everything intelligently, and lets clients talk directly to storage nodes, eliminating central controllers and bottlenecks.
In short: Ceph is the technology and architecture that powers modern distributed storage.
What is Ceph Storage?
Ceph storage is the real-world, deployed Ceph cluster—the combination of commodity hardware and the Ceph software stack—delivering usable block, file, or object storage.
Common examples:
- Hyperconverged Ceph cluster inside Proxmox or OpenStack
- External Ceph cluster providing RBD block devices or CephFS shared filesystems
- Dedicated Ceph RGW deployment offering S3-compatible object storage
- Large-scale backend for Kubernetes/OpenShift persistent volumes
If Ceph is the engine, Ceph storage is the fully built and tuned vehicle ready for production workloads.
What are Ceph’s features?
Ceph provides unified object-based storage, automatic healing, no single point of failure, and near-linear scalability across distributed nodes.
| Feature | Description |
Object-based storage |
All data (block, file, object) is stored as objects in a flat namespace |
CRUSH algorithm |
Deterministic, pseudo-random placement function — no lookup tables needed |
No single point of failure |
Fully distributed monitors, metadata servers, and data placement |
Self-healing & self-managing |
Automatic detection, rebalancing, and recovery of failed nodes/drives |
Linear scalability |
Performance and capacity scale near-linearly by adding more OSD nodes |
Unified storage |
Same cluster can simultaneously serve block (RBD), file (CephFS), and object (RGW) storage |
Strong consistency (optional) |
Configurable replication or erasure coding with tunable consistency levels |
How does Ceph store and locate data?
Ceph stores data as objects in placement groups mapped deterministically to OSDs using the CRUSH algorithm.
| Component | Description |
Object |
Fixed or variable-size chunk of data with a unique identifier |
Placement Group (PG) |
Logical bucket that groups objects for replication/erasure coding and distribution |
OSD |
One disk (or NVMe/SSD) running an OSD daemon — stores objects, handles replication & recovery |
CRUSH map |
Cluster map + ruleset that tells the system exactly where each PG (and therefore each object) belongs |
Clients and OSDs use the same CRUSH function. Anyone can calculate where data lives without consulting a central index.
How does Ceph manage metadata?
File system metadata (CephFS) is handled by a cluster of Metadata Servers (MDS).
Modern Ceph (Luminous and later) supports:
- Multiple active MDS daemons (commonly 3–32+ in large clusters)
- Automatic rank balancing and failover
- In-memory caching with lazy persistence to RADOS
- Separate journaling pool on fast storage for maximum performance
This design scales to millions of IOPS and billions of files without the legacy dynamic subtree partitioning bottlenecks.
What makes Ceph’s data placement unique?
CRUSH (Controlled, Scalable, Decentralized Placement of Replicated Data) is the heart of Ceph’s scalability.
| Benefit | Explanation |
No allocation tables |
Eliminates metadata bottleneck |
Minimal data movement on cluster change |
Adding/removing nodes moves only ~1/num_PGs fraction of data |
Failure-domain awareness |
Rules can separate replicas across racks, rows, data centers, etc. |
Weighted capacity handling |
Larger/faster drives automatically receive more data |
Client-driven placement |
Clients compute placement themselves → direct I/O to OSDs, no proxy |
How does Ceph handle failure and recovery?
- Every object belongs to a placement group that is replicated or erasure-coded across multiple OSDs
- OSDs continuously heartbeat and peer with each other
- On failure, surviving OSDs immediately promote new primaries and begin parallel backfill/recovery
- Cluster remains fully available during recovery (degraded mode)
- Recovery traffic is throttled and prioritized to avoid impacting client workloads
How well does Ceph scale?
Ceph scales nearly linearly in capacity, metadata throughput, and client concurrency simply by adding nodes.
| Metric | Scaling Behavior |
Capacity & throughput |
Near-linear with added OSDs (10 GbE → 100 GbE+ networks now common) |
Metadata performance |
Near-linear with additional active MDS nodes |
Concurrent clients |
Tens of thousands of clients supported without gateways or load balancers |
Real-world deployments |
Production clusters from <10 nodes to >10,000 OSDs and exabytes of storage (Meta, CERN, Bloomberg, etc.) |
Who is Ceph best suited for?
Ceph shines when you need:
- Petabyte-to-exabyte scale on commodity hardware
- Mixed block + file + object workloads from the same cluster
- High availability with no single point of failure
- Frequent cluster growth/shrink and hardware churn
- Kubernetes/OpenShift, OpenStack, Proxmox, or private cloud environments
- S3-compatible object storage for AI, analytics, backups, archives
How does HorizonIQ use Ceph for our Proxmox Managed Private Cloud and storage environments?
At HorizonIQ, Ceph is the backbone of our Proxmox Managed Private Cloud. In our Proxmox clusters, we typically run a hyperconverged Ceph design: each compute node includes NVMe drives dedicated to Ceph, with no RAID controller in the path to reduce latency.
Ceph handles data resilience through replication (we standardize on three replicas), so if a drive fails, the cluster automatically rebuilds from healthy copies while workloads keep running. You would need multiple, overlapping failures across nodes before data is at risk, which is extremely unlikely given our hardware SLAs and fast replacement process.
These same Ceph foundations are offered across our dedicated block and object storage platforms. With Ceph enabled, our block storage tiers deliver strong, predictable performance for VMs and databases.
Our object storage clusters can leverage Ceph as well, delivering high throughput, exceptional durability, and scalable S3-compatible storage built for AI, analytics, and large datasets.
Across private cloud, block storage, and object storage, Ceph enables HorizonIQ to deliver high availability, consistent performance, and flexible scaling. Our goal is to give customers the ability to choose the architecture and growth model that fits their environment.
