Storage capacity remains a critical concern in modern datacenters. Organizations want to host more and more workloads, while physical storage growth is often expensive or limited. VMware vSAN addresses this challenge with a range of space efficiency technologies that help reduce costs and improve performance.
Opportunistic vs. Deterministic Techniques
The whitepaper distinguishes between two categories of techniques:
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Opportunistic: dependent on the characteristics of the data, which means savings are not guaranteed. Examples include deduplication & compression (OSA), compression-only, thin provisioning, and TRIM/UNMAP space reclamation.
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Deterministic: delivers predictable and guaranteed space savings. This is the case with RAID-5/6 erasure coding.
Both types can be used independently or combined to maximize efficiency.
ESA versus OSA
With the introduction of the vSAN Express Storage Architecture (ESA) in vSAN 8, the options have significantly improved. While the Original Storage Architecture (OSA) had limitations around performance and deduplication domains, ESA provides much more effective data reduction without noticeable performance trade-offs.
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Compression in ESA: Data is compressed as soon as it enters the vSAN stack, reducing CPU load and network traffic.
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Global Deduplication in ESA: The deduplication domain spans the entire cluster, making data reduction far more effective than OSA’s per–disk group approach.
For existing environments still running on OSA, deduplication & compression or compression-only remain valid options, but they come with more performance considerations.
Thin Provisioning and TRIM/UNMAP
With thin provisioning, storage is only allocated when actually needed. This allows oversubscription, a common practice to make better use of capacity.
A well-known drawback is that released space inside a VMDK is not automatically reclaimed. TRIM/UNMAP solves this issue by freeing unused blocks. This not only increases usable capacity but also speeds up recovery and rebalance operations.
Erasure Coding: RAID-5 and RAID-6
Where RAID-1 mirroring always creates a full copy of the data—consuming large amounts of storage—erasure coding provides a more efficient alternative.
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RAID-5 (FTT=1) consumes 1.33x the original data in OSA, or just 1.25x in ESA.
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RAID-6 (FTT=2) consumes 1.5x the original data, compared to 3x with mirroring.
In ESA, these techniques are available without any performance trade-offs, making them the logical standard for most environments.
Conclusion
By combining opportunistic and deterministic space efficiency techniques, vSAN allows organizations to use storage more intelligently and cost-effectively. Especially with ESA, both performance and efficiency are greatly enhanced. For environments still running OSA, migrating to ESA is a worthwhile step to optimize both capacity and performance.
Want to learn more?
For a deep dive into all the available techniques, trade-offs, and configuration details, get a copy of the full whitepaper.
