When to use: Size SAN, NAS, or server-attached storage arrays. Input raw capacity and RAID level to find usable space after parity overhead. Applies deduplication and compression ratios to estimate effective capacity, then projects raw storage needed to accommodate multi-year growth.
This calculator determines usable SAN or NAS capacity after RAID overhead, applies deduplication and compression ratios to estimate effective capacity, and projects the raw storage required to meet multi-year growth targets. Storage engineers use it during system design and refresh planning to right-size arrays before procurement.
Raw capacity is the total disk space before any redundancy scheme. RAID overhead varies by level: RAID 5 loses one disk worth of capacity (usable = (N-1)/N of raw), RAID 6 loses two disks ((N-2)/N), RAID 1 mirrors every disk (50% usable), and RAID 10 mirrors then stripes (50% usable with better read IOPS). The raw usable space is then multiplied by deduplication and compression ratios to yield effective capacity — the actual amount of unique data the array can hold.
Growth projection uses compound annual growth: future_raw = raw × (1 + growth_rate)^years. This gives the raw capacity required today to support the predicted data volume at the end of the planning horizon without purchasing additional hardware. Industry planning horizons are typically 3–5 years.
RAID levels are defined by SNIA (Storage Networking Industry Association) specifications. iSCSI SAN protocol is standardized in RFC 3720. Fibre Channel SAN is governed by T11 standards (FC-PI, FC-FS). NAS protocols NFS v3/v4 (RFC 1813, RFC 7530) and SMB/CIFS (MS-SMB2) govern network file access. SNIA's Swordfish API (DMTF DSP2046) provides a standard interface for storage management. For healthcare and financial data, retention and availability requirements are governed by HIPAA, SOX, and SEC Rule 17a-4, which mandate immutable storage (WORM) for specific record types.
Deduplication ratios vary significantly by data type: virtual machine datastores achieve 3:1 to 5:1 dedup, databases and compressed files achieve 1:1 to 1.5:1, and backup data achieves 10:1 to 20:1 with global dedup across backup sets. Compression ratios similarly depend on data type — text and log data compress 3:1 to 5:1, while already-compressed media (JPEG, MP4, ZIP) compress at nearly 1:1. RAID 5 with 3 disks provides only 1 disk of usable space and is vulnerable to unrecoverable read errors (URE) during rebuild on large drives; RAID 6 or RAID-DP is strongly recommended for drives larger than 2 TB. Always maintain a hot spare drive in large arrays to begin automatic rebuild immediately after a drive failure.
Enter the raw storage capacity of your planned array and the individual drive size. Select the RAID level that matches your redundancy requirements. Set dedup and compression ratios based on your workload profile — use 1.0 for databases and media, and higher values for VM and backup workloads. Enter the annual data growth rate (obtain from your capacity management records or estimate 20–30% for typical enterprise). The calculator shows usable capacity, effective capacity with data reduction, and the raw storage needed at the end of your planning horizon.
RAID 5 uses one parity disk distributed across all drives, tolerating one simultaneous drive failure. RAID 6 uses two distributed parity sets, tolerating two simultaneous failures. For drives larger than 2 TB, RAID 6 is recommended because the probability of a second drive failure during rebuild (which can take 12–48 hours for large drives) exceeds acceptable risk.
Deduplication identifies and removes identical data blocks across the entire storage pool, storing only one copy and pointers to it. Compression reduces the size of individual data blocks using algorithms like LZ4 or gzip. Both are measured as ratios: 2:1 means 2 TB of logical data stored in 1 TB of physical space. They are typically applied together.
IOPS depends on drive type: 7,200 RPM SATA HDDs deliver approximately 75–100 IOPS, 15,000 RPM SAS HDDs deliver 150–200 IOPS, SATA SSDs deliver 50,000–100,000 IOPS, and NVMe SSDs deliver 500,000–2,000,000 IOPS. Enterprise databases require 2,000–10,000 IOPS per server; size the array's disk count accordingly.
Typical enterprise storage growth is 20–30% per year for general file servers and VMs. Big data and analytics environments grow 50–100% per year. Video surveillance storage grows in proportion to camera count and retention period increases. Use 3 years of actual capacity data from your monitoring tools for the most accurate projection.
SAN (FC or iSCSI block storage) is required for database workloads requiring low latency, VMware VMFS datastores, and applications needing raw block device access. NAS (NFS, SMB) is appropriate for file sharing, home directories, and application data that uses file system semantics. Hyper-converged infrastructure (HCI) blurs this distinction by providing both block and file services from the same platform.
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