vSAN capacity calculator
Raw → usable capacity. Accounts for RAID overhead, slack space, and FTT.
6
60 TB
Capacity breakdown
Total raw capacity
360 TB
After RAID overhead
240 TB
3:2 ratio (66.7% efficient)
Usable capacity (25% slack)
180 TB
VMware recommends 25-30% slack for performance
Plan against
180 TB
Maximum workload data you should plan to store
Architecture notes
- OSA (Original Storage Architecture): cache + capacity tiers, vSAN 7 and earlier.
- ESA (Express Storage Architecture): flat NVMe pool, vSAN 8+. Better RAID-5/6 performance.
- FTT (Failures to Tolerate): how many node failures the cluster can survive without data loss.
- Slack space: vSAN needs free space for rebuild and rebalance operations.