While the DD&C process occurs after the write acknowledgment is sent to the guest VM, enabling it in vSAN can impact performance under certain circumstances, which will be discussed below. It also avoids the challenges of deduplicating data already at rest. Implementing DD&C in this manner prevents the performance penalties found with inline systems that perform the deduplication prior to sending the write acknowledgment back to the guest. Otherwise, it will leave as-is, and continue destaging the data to the capacity tier. If the 4KB block can be compressed by 50% or more, it will do so. This task is followed by the compression process. Minimizing any form of data manipulation until after the acknowledgment has been sent help keeps write latency seen by the guest VM low.Īs data is destaged, the deduplication process will look for opportunities to deduplicate the 4KB blocks of data it finds within a disk group: vSAN's deduplication domain. The process occurs as the data is destaged to the capacity tier - well after the write acknowledgments have been sent back to the VM. The degree to which the savings will occur will be highly dependent on the technology in place, the workloads, and even the host hardware configuration.ĭeduplication and compression (DD&C) in vSAN is enabled at the cluster level, as a single space efficiency feature.
If a given set of conditions is ideal for saving capacity, it will do so based on that given set of conditions. Opportunistic space efficiency techniques do just as the name implies. The specific trade-offs when doing so will be discussed in this document. In vSAN, opportunistic and deterministic space efficiency features can be used independently or together. vSAN offers deterministic space efficiency capabilities through data placement schemes that are optimized for storing data in a resilient but efficient manner. These space efficiency techniques can be relied upon to deliver a guaranteed level of capacity savings. vSAN offers several types of opportunistic space efficiency features such as Deduplication & Compression, Compression-only, TRIM/UNMAP space reclamation, and thin provisioning. These space efficiency techniques are dependent on conditions of the data, and not guaranteed to return a predetermined level of savings. Space efficiency techniques can be categorized into the following: VMware vSAN has several technologies in place to help improve storage efficiency. Space efficiency technologies in enterprise storage play an important role improving value and decreasing costs.
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