Why your 2024 vSAN sizing assumptions no longer hold against VCF 5.2.

The VCF 5.2 release shipped through the second half of 2025 and is now the default subscription artifact on every North America and EMEA renewal the Desk has reviewed in 2026. The release changes the unit definitions for vSAN inside VCF in ways that invalidate the sizing model most enterprise buyers carried out of the 2024 cycle. The buyer who walks into the 2026 renewal carrying the 2024 sizing spreadsheet and the 2024 negotiation playbook arrives with a model that produces the wrong number in two places. The first place is the size the buyer asks for. The second place is the price band the buyer expects. This article works the five assumptions that have inverted, in order of revenue impact on the renewal.

Two preliminary notes. First, this article is about subscription contracts. The perpetual licence cohort still exists on the Desk's book and the dynamics are different. Second, the article is about vSAN inside VCF. Standalone vSAN follows a similar pattern but the bundled inclusion changes the calculus on the second and fourth assumptions below. Where the difference matters the article calls it out.

The five assumptions inverted, ordered by the dollar impact on the median 2026 renewal, are: raw to usable ratio, snapshot reservation accounting, encryption overhead allocation, deduplication credit treatment, and the cross cluster capacity pool. The buyer who carries the 2024 model on any one of these into the 2026 conversation loses ground. The buyer who carries the 2024 model on all five loses more ground than the 2024 model itself ever cost to build.

One: raw to usable ratio inverted on default policy

The 2024 model anchored the raw to usable ratio on a default RAID 1 policy with a mirror factor of two and a per object capacity reservation that left the buyer at roughly 0.45 usable to raw. The 2024 sizing question was whether the buyer was willing to move the cluster to RAID 5 with erasure coding to recover usable capacity. The 2024 buyer often declined on operational risk grounds. The 2026 default policy in VCF 5.2 inverts the question. The default has moved toward an erasure coded posture for clusters above a threshold node count, with the mirror posture retained as the option for smaller clusters and for specific workload classes. The buyer who applies the 2024 mental model overbuys raw capacity by between 18 and 32 percent on the median estate the Desk has reviewed in 2026.

The renegotiation move is to require the seller's quote engine to size the renewal against the policy the cluster will actually run at term start, not the policy the cluster ran at term start of the prior cycle. The seller's deal desk has no incentive to volunteer this. The buyer asks in writing, anchored to the configuration export.

Two: snapshot reservation accounting

The 2024 model treated snapshot reservation as a small percentage adder, typically 5 to 8 percent of usable, allocated as a sizing buffer. The 2026 release reorganises the snapshot accounting at the storage policy level, allowing the snapshot reservation to be drawn from a shared pool rather than a per object allocation. The buyer who carries the 2024 adder into the 2026 sizing produces a model that overstates the renewal by the difference. On the median estate the difference is between 4 and 7 percent of usable, which is between 8 and 15 percent of raw at the new policy defaults.

The standalone vSAN cohort does not see this change. The shared snapshot pool is a VCF integration artifact. For bundled buyers it is the second largest single source of overbuy in the 2024 sizing carryover.

Three: encryption overhead allocation

The 2024 model accounted for encryption overhead as a flat percentage allocation against usable, sized at 3 to 5 percent on most estates. The 2026 release changes the placement of the encryption overhead from the data path to the metadata path for the majority of object classes, with a corresponding reduction in the visible capacity overhead. The buyer who carries the 2024 allocation arrives at a usable number that is 3 to 5 percent low on the median estate, which translates directly to a renewal anchor that is too high by the same percentage on the seller's quote. The number is not material on a small estate. It is material at scale. On a 4 petabyte renewal the differential is between $300,000 and $600,000 per year at the median realised unit price.

"The 2024 sizing model and the 2026 quote engine are speaking different languages. The buyer who translates from one to the other before the renewal opens is buying back five assumptions worth of position. The buyer who does not translate is handing the seller the differential."VCF Engagement Lead, The Desk

Four: deduplication credit treatment

The 2024 model treated deduplication and compression credit as a sizing tailwind, with the buyer typically holding 1.3 to 1.6 times the raw capacity in addressable workload. The 2026 release changes the credit treatment in two ways. First, the credit is now accounted against the policy class rather than the cluster, which means the buyer must sum the credit per policy rather than apply it as a cluster wide multiplier. Second, the credit is no longer assumed at sizing time. The seller's quote engine requires the buyer to bring documented dedupe ratios to apply the credit, where in 2024 the credit was applied as a planning assumption. This is the inversion. The 2024 buyer received credit by default. The 2026 buyer receives credit by document.

The remediation is straightforward and most enterprises do not do it. The buyer runs a 30 day dedupe and compression measurement at the policy level, exports the ratio per policy class, and brings the export to the quote engine. The seller's deal desk applies the credit on production of the document. On the median estate, the document is worth between 7 and 12 percent off the renewal anchor. The cost of producing the document is between two and five operations hours. The return on the document is the largest single hour return in the entire VCF renewal toolkit.

Five: cross cluster capacity pool

The 2024 model sized vSAN per cluster, with the buyer paying for the capacity inside each cluster individually. The 2026 release introduces a cross cluster capacity pool inside VCF that allows entitled capacity to be drawn across clusters within the same VCF instance, subject to topology constraints. The buyer who continues to size per cluster overbuys the aggregate by the difference between the per cluster maximum and the cross cluster mean. On a multi cluster estate that is between 8 and 14 percent of total capacity on the median configuration. The smaller the cluster count, the smaller the differential. The larger the cluster count, the more material it becomes.

This change is the assumption that is hardest to retrofit into a 2024 sizing spreadsheet because the spreadsheet was structured per cluster. The renegotiation move is to rebuild the sizing at the VCF instance level rather than the cluster level, and to take the per instance number into the quote conversation. The seller's deal desk has the documentation to support the pool. The buyer's procurement team often does not have the model. The Desk's view is that this is the single largest sizing dollar opportunity on multi cluster 2026 renewals and is the one most often left on the table.

The reason the cross cluster pool is so often missed is that the procurement and architecture teams are looking at different documents. Architecture is looking at the cluster topology. Procurement is looking at the renewal quote. Neither sees the instance level pool unless someone holds both views at the same time. The Desk's first move on every multi cluster renewal is to put the architecture topology export and the renewal quote side by side and to run the pool calculation. That single calculation has produced more renewal value across the 2026 book than any other single procedural move on VCF.

What the 2026 model looks like end to end

The five assumptions stack. The buyer who corrects all five sees a sizing model that is between 22 and 41 percent smaller than the 2024 model would have produced on the same physical estate. The 22 percent end of the band is a small estate with one or two clusters and no encryption. The 41 percent end is a large multi cluster estate with encryption, snapshots in policy use, and dedupe ratios above 1.4. The median is 31 percent. The seller's quote engine has no incentive to volunteer this. The buyer who asks for the sizing in writing, with the five corrections applied, recovers the position the 2024 model had given away.

What we have seen on live deals

A North America Fortune 200 buyer brought a 2026 VCF renewal to the Desk in January with a sizing spreadsheet carried forward from the 2024 cycle. The opening quote was anchored to 5.4 petabytes raw across nine clusters. The Desk rebuilt the sizing at the VCF instance level against VCF 5.2 defaults, with a 30 day dedupe export and a current policy configuration export. The corrected size was 3.8 petabytes raw, a 29 percent reduction on the original. The renewal cleared at the corrected size on the same scope and same term. The buyer did not change the physical estate. The buyer changed the sizing document. The differential was the artefact of the document, not the artefact of the architecture.

The takeaway

• The 2024 vSAN sizing model does not translate to a VCF 5.2 quote. Five assumptions have inverted. The buyer who carries the old model arrives at a number that is between 22 and 41 percent too large on the median estate.
• Three of the five corrections require buyer documents: a current policy export, a 30 day dedupe measurement, and a per instance topology export. None take longer than a week. All produce material renewal value.
• The single most actionable correction is the cross cluster capacity pool on multi cluster estates. It is also the one most often missed because the 2024 sizing spreadsheet has no row for it.