{
    "name": "RAID Rebuild Time Calculator",
    "url": "https://calculators.geekmidst.com/calculators/raid-rebuild-time-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/raid-rebuild-time-calculator.md",
    "category": "IT, networking & security",
    "description": "Estimate how long a RAID array takes to rebuild onto a replacement drive from its capacity, the rebuild rate in MB/s and how much of it must be rewritten.",
    "summary": "A rebuild rewrites the replacement drive from the survivors, so its length is the data to rebuild divided by the sustained rebuild rate. Long rebuilds are the window in which a second failure hurts most.",
    "also_called": [
        "RAID resilver time calculator",
        "Array rebuild calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "drive_size",
            "label": "Drive capacity",
            "type": "number",
            "default": "12"
        },
        {
            "name": "size_unit",
            "label": "Size unit",
            "type": "segmented",
            "default": "TB",
            "options": {
                "TB": "TB",
                "GB": "GB"
            }
        },
        {
            "name": "rate_mbs",
            "label": "Sustained rebuild rate",
            "type": "number",
            "default": "150",
            "unit": "MB/s"
        },
        {
            "name": "fill_percent",
            "label": "Share of the drive to rebuild",
            "type": "number",
            "default": "100",
            "unit": "%"
        }
    ],
    "outputs": [
        {
            "key": "hours",
            "label": "Rebuild time",
            "format": "number"
        },
        {
            "key": "duration",
            "label": "Rebuild time",
            "format": "text"
        },
        {
            "key": "days",
            "label": "Rebuild time",
            "format": "number"
        },
        {
            "key": "data_tb",
            "label": "Data rewritten",
            "format": "number"
        }
    ],
    "formula": {
        "text": "Time (s) = Drive capacity (bytes) × Share ÷ (Rate × 10⁶ bytes/s)",
        "variables": {
            "Drive capacity": "decimal: 1 TB = 10¹² bytes",
            "Rate": "megabytes (10⁶ bytes) per second"
        }
    },
    "worked_example": {
        "inputs": {
            "drive_size": "12",
            "size_unit": "TB",
            "rate_mbs": "150",
            "fill_percent": "100"
        },
        "steps": [
            "12 TB = 12 × 10¹² bytes.",
            "12 × 10¹² ÷ 150 × 10⁶ bytes/s = 80,000 s.",
            "80,000 ÷ 3,600 = 22.22 hours."
        ],
        "result": "Rebuilding a 12 TB drive at 150 MB/s takes about 22 hours."
    },
    "interpretation": "If the rebuild takes days, consider RAID 6 or triple parity so a second failure during the rebuild is survivable, and keep a hot spare so the rebuild starts at once.",
    "assumptions": [
        "The rebuild rate stays constant from start to finish."
    ],
    "limitations": [
        "Production I/O, controller rebuild-priority settings and SMR drives can make real rebuilds several times slower."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why is my rebuild slower than the drive’s rated speed?",
            "answer": "Controllers throttle rebuilds to keep the array responsive, and every surviving drive must be read in parallel. Random-access workloads during the rebuild slow it further."
        },
        {
            "question": "Does a RAID 10 rebuild faster than RAID 5?",
            "answer": "Usually: RAID 10 copies from one mirror partner, while RAID 5 and 6 read all surviving drives and compute parity."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "RAID Capacity Calculator",
            "url": "https://calculators.geekmidst.com/calculators/raid-capacity-calculator"
        },
        {
            "name": "Database Backup Window Calculator",
            "url": "https://calculators.geekmidst.com/calculators/database-backup-window-calculator"
        },
        {
            "name": "Download Time Calculator",
            "url": "https://calculators.geekmidst.com/calculators/download-time-calculator"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}