ZFS vs Ceph: Do You Actually Need Ceph? 

Two Strong Contenders 

Ceph and ZFS solve very different problems, despite often appearing at the top of the list during storage platform discussions. While both provide data integrity, snapshots, and asynchronous replication, the type of scalability they provide is quite different. Both are open source and widely deployed in production environments. It is simply just a matter of determining which is right for your environment. 

Ceph is a distributed storage system designed to aggregate a large number of servers into a single storage namespace. ZFS, on the other hand, is a local filesystem and volume manager designed to scale by adding additional storage to a single large server, while extracting maximum performance, reliability, and simplicity from that storage system. 

Understanding Your Requirements 

Organizations frequently compare these two technologies because each can be used as the foundation of successful virtualization, backup, database, and general-purpose storage environments. In the end, the question is not which technology is universally better but is whether your environment requires a fully distributed storage system with the trade-offs that entails. 

In many cases, ZFS delivers better performance, lower latency, simpler operations, and a lower total cost of ownership because it takes a far more direct approach. Reducing operational complexity while maintaining the required level of durability and high availability can make ZFS the more compelling option even for the most demanding workload. 

Ceph has its advantages, primarily the ability to scale beyond what a single machine can achieve and to maintain data durability in the face of multiple node failures. These features come at a cost, in both complexity and minimum scale, as well as the higher latency and performance overhead required by its distributed nature. If your environment requires these features, it may be that you do not have a choice but to make these trade-offs. However, as the performance that can be achieved with a single node continues to expand with dozens or hundreds of cores and faster PCI-e generations, and with strong high-availability fail-over capabilities, ZFS can survive the failure of a single node without the level of orchestration and overhead required by Ceph. Does your environment need to be able to scale to 1000s of disks or the loss of multiple servers to achieve its goals? Or would an easier to understand, faster to recover, lower latency storage system be a better fit?

The Cost of Distributed Systems 

Distributed systems are one of the most notoriously complex subjects within computer science, making them difficult to design, deploy, and operate. The trade-off for these additional costs is the unique capabilities that standalone systems cannot provide. A Ceph cluster can survive the loss of multiple servers while continuing to provide access to data. Capacity and performance can be expanded horizontally by adding additional nodes to the system, and the workloads are spread across the entire cluster.These benefits, however enticing, come with costs. 

Every write in Ceph involves network communication, replication or erasure coding, placement calculations, cluster state management, and coordination between multiple daemons. In order to provide data durability, each write must wait until it is safely on non-volatile media on the majority of the nodes before it can safely complete. Even simple operations may require communication between several nodes before they can be acknowledged or completed. 

By contrast, ZFS systems do not have these requirements. When an application writes data to ZFS, the filesystem writes directly to local storage devices. There is no network hop, no distributed consensus or elections, and no requirement to coordinate with other servers. The result is a shorter I/O path and less overhead between the application and the underlying media. ZFS can further reduce latency by acknowledging writes as soon as they are on non-volatile storage, even if that storage is not the intended destination of the write. Once data is safe, ZFS allows the application to move forward, rather than be stuck waiting for the full write to complete. 

This difference becomes particularly important for latency-sensitive workloads such as databases and virtual machines. 

Latency Matters More Than Bandwidth 

Many storage evaluations focus on aggregate throughput, how many gigabytes per second can the storage infrastructure deliver. While bandwidth is important, latency often has a far greater impact on application performance and user experience. 

Databases, virtualization platforms, build systems, and transaction-processing applications frequently issue large numbers of small random I/O operations. These workloads are limited by latency long before they exhaust available bandwidth. If the next operation cannot start because it depends on the data from the previous I/O, no amount of bandwidth will make that operation any faster. 

In a Ceph environment, every operation must traverse the network and pass through multiple software layers. Modern networks are fast, but they are still slower than accessing local storage directly. When deploying storage for a hypervisor, the additional round trips over the network limit the performance that can be achieved, even when mitigated with high levels of concurrency. 

A ZFS storage server equipped with NVMe devices can often deliver much lower latency than a Ceph cluster using the same hardware. This is not because Ceph is poorly designed, but because distributed systems necessarily introduce additional work that ZFS was able to avoid. 

The trade-off in a distributed system only makes sense when the benefits of distribution outweigh the performance and latency costs. For many workloads, they do not. 

Simplicity Has Operational Value 

Storage failures are often operational failures rather than hardware failures. Complex systems require more monitoring, more expertise, and more maintenance. Every additional component becomes another potential source of outages, misconfigurations, or performance problems. 

Let’s compare the operational and deployment complexity of these two storage systems: 

Consider that each component must be understood, monitored, upgraded, and maintained. By comparison, a ZFS-based storage appliance can often be operated by a much smaller team. Administrators manage pools, datasets, snapshots, replication, and storage devices without needing to understand the behavior of a distributed system or cluster.

This simplicity has practical consequences. Troubleshooting becomes easier because there are fewer moving parts. Upgrades become easier because fewer services are involved. Capacity planning becomes easier because data is not constantly being redistributed across nodes in a cluster. 

Organizations frequently underestimate the cost of operational complexity until they have to support it for years. 

When Ceph Is the Better Choice 

None of this means Ceph should be avoided. Ceph excels when organizations genuinely need distributed storage. However, many organizations fall into the trap of thinking they need a cluster when they would be better served by a much less complex, yet highly available ZFS storage system.

Some examples of deployments that need a distributed system include: 

• 10+ petabyte environments 

• Large private clouds (1000+ VMs) 

• Environments requiring storage across many servers and locations 

• Workloads requiring scaling of capacity and performance (10s of billions of objects) 

• Platforms where multiple server failures must be transparent to applications 

These are problems ZFS was not designed to solve by itself. Attempting to replace a large-scale distributed storage platform with standalone storage servers would simply move complexity elsewhere. 

Choosing the Right Tool 

Storage architecture should be driven by requirements rather than trends. If the requirement is distributed storage across many nodes, Ceph remains one of the most capable open-source platforms available. If the requirement is reliable, high-performance storage with low latency and straightforward operations, ZFS is often the better choice. 

 Many organizations turn to distributed storage believing it is necessary to achieve scale. In reality, modern servers can deliver extraordinary amounts of capacity and performance. A single system with high-density flash storage can often satisfy workloads that previously required huge clusters. 

Before accepting the complexity of a distributed storage platform, it is worth asking a simple question: does this workload actually require distributed storage? If the answer is no, ZFS often provides a faster, simpler, and more efficient solution. 

The best storage platform is the one that solves your actual requirements with the least complexity. Klara has helped organizations around the world architect, deploy, and support OpenZFS-powered infrastructure for virtualization, databases, back up, and enterprise storage. Whether you are evaluating OpenZFS vs Ceph, or looking to optimize your existing storage deployment, Klara’s Infrastructure support can help you design a storage platform that delivers the performance, reliability, and simplicity your environment needs.