{"id":67247,"date":"2026-10-20T13:06:01","date_gmt":"2026-10-20T10:06:01","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=67247"},"modified":"2026-10-20T13:06:01","modified_gmt":"2026-10-20T10:06:01","slug":"raid-calculator-usable-capacity","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/web-tools\/raid-calculator-usable-capacity\/","title":{"rendered":"RAID Calculator \u2013 Usable Capacity"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">Find the Usable Capacity of Your RAID Array<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"67247\" data-favorite-title=\"RAID\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/web-tools\/raid-calculator-usable-capacity\/\" data-favorite-excerpt=\"Enter your RAID level, drive count and drive size to find the usable capacity, raw capacity, array efficiency, fault tolerance and estimated speed of your RAID array. Covers RAID 0, 1, 5, 6, 10, 50, 60 and JBOD.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-window-code\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/web-tools\/raid-calculator-usable-capacity\/\" method=\"POST\" class=\"calculator\" id=\"calculator-67247\" data-post=\"67247\"><fieldset class=\"fieldset-input is-2\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field is-single\" id=\"input-1\"><label for=\"field-1\">RAID level<\/label><div class=\"grid grid-cols-1\"><select id=\"field-1\" name=\"raid_level\"><option value=\"raid0\">RAID 0 \u2013 striping, no redundancy<\/option><option value=\"raid1\">RAID 1 \u2013 mirroring<\/option><option value=\"raid5\" selected>RAID 5 \u2013 single parity<\/option><option value=\"raid6\">RAID 6 \u2013 double parity<\/option><option value=\"raid10\">RAID 10 \u2013 mirrored stripes<\/option><option value=\"raid50\">RAID 50 \u2013 striped RAID 5 sets<\/option><option value=\"raid60\">RAID 60 \u2013 striped RAID 6 sets<\/option><option value=\"jbod\">JBOD \u2013 just a bunch of drives<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-2\">Number of drives<\/label><div class=\"term\">n<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"number_of_drives\" id=\"field-2\" aria-describedby=\"calc-info-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"1\" max=\"256\" value=\"6\"\/><small id=\"calc-info-2\">All drives are assumed to be the same size.<\/small><\/div><div class=\"field\" id=\"input-3\"><label for=\"field-3\">Drive size<\/label><div class=\"field-group\"><input type=\"text\" name=\"drive_size\" id=\"field-3\" aria-describedby=\"calc-info-3\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0.001\" value=\"4\"\/><div class=\"grid grid-cols-1\"><select id=\"field-4\" name=\"unit\" aria-label=\"Unit\"><option value=\"GB\">GB<\/option><option value=\"TB\" selected>TB<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-3\">Decimal storage units: 1 TB = 1000 GB.<\/small><\/div><div class=\"field has-term\" id=\"input-4\" hidden><label for=\"field-5\">Number of groups<\/label><div class=\"term\">g<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"number_of_groups\" id=\"field-5\" aria-describedby=\"calc-info-5\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"2\" max=\"32\" value=\"2\"\/><small id=\"calc-info-5\">RAID 50\/60 only: equal groups, each with at least 3 (RAID 50) or 4 (RAID 60) drives.<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"67247\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Capacity and Performance<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Usable capacity<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"TB\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-2\"><span class=\"field-title\"><span>Usable capacity<\/span><\/span><span class=\"field-value\" id=\"result-2\" data-unit=\"TiB\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-3\"><span class=\"field-title\"><span>Raw capacity<\/span><\/span><span class=\"field-value\" id=\"result-3\" data-unit=\"TB\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-4\"><span class=\"field-title\"><span>Array efficiency<\/span><\/span><span class=\"field-value\" id=\"result-4\" data-unit=\"%\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-5\"><span class=\"field-title\"><span>Fault tolerance<\/span><\/span><span class=\"field-value\" id=\"result-5\" data-unit=\"drives\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-6\"><span class=\"field-title\"><span>Relative read speed<\/span><\/span><span class=\"field-value\" id=\"result-6\" data-unit=\"\u00d7\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-7\"><span class=\"field-title\"><span>Relative write speed<\/span><\/span><span class=\"field-value\" id=\"result-7\" data-unit=\"\u00d7\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-8\"><span class=\"field-title\"><span>Minimum drives required<\/span><\/span><span class=\"field-value\" id=\"result-8\" data-unit=\"drives\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result is-column\" id=\"output-9\"><span class=\"field-title\"><span>Array summary<\/span><\/span><span class=\"field-value\" id=\"result-9\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"67247\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>RAID Usable Capacity Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[ \\begin{aligned} \\text{RAID 0, JBOD: } &amp; U = n \\cdot s \\\\ \\text{RAID 1: } &amp; U = s \\\\ \\text{RAID 5: } &amp; U = (n-1) \\cdot s \\\\ \\text{RAID 6: } &amp; U = (n-2) \\cdot s \\\\ \\text{RAID 10: } &amp; U = \\frac{n}{2} \\cdot s \\\\ \\text{RAID 50: } &amp; U = (n-g) \\cdot s \\\\ \\text{RAID 60: } &amp; U = (n-2g) \\cdot s \\end{aligned} \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(U\\) \u2014 usable capacity of the array<\/li>\n<li>\\(n\\) \u2014 number of drives in the array<\/li>\n<li>\\(s\\) \u2014 size of one drive (all drives assumed to be identical)<\/li>\n<li>\\(g\\) \u2014 number of equal sub-groups (RAID 50 and RAID 60 only)<\/li>\n<\/ul>\n<p>Usable capacity is the space left for data after redundancy is set aside: the number of drives' worth of capacity that survives, multiplied by the drive size. RAID 0 and JBOD keep everything, mirroring levels give up half the drives, and parity levels sacrifice one or two drives' worth per group.<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>RAID Usable Capacity \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> a RAID 5 array built from 6 identical 4 TB drives \u2014 the calculator's default values.<\/p>\n<p>\\[ U = (n-1) \\cdot s = (6-1) \\times 4\\ \\text{TB} = 20\\ \\text{TB} \\]<\/p>\n<p>\\[ \\text{efficiency} = \\frac{20\\ \\text{TB}}{6 \\times 4\\ \\text{TB}} \\times 100\\% \\approx 83.33\\% \\]<\/p>\n<p><strong>Result:<\/strong> 20 TB usable (about 18.19 TiB) out of 24 TB raw, with tolerance for a single drive failure. Estimated sequential speed: 6\u00d7 read and 1.25\u00d7 write relative to one drive.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the RAID Calculator<\/h2>\n<ol>\n<li>Select the <strong>RAID level<\/strong> (RAID 0, 1, 5, 6, 10, 50, 60 or JBOD).<\/li>\n<li>Enter the <strong>Number of drives<\/strong> in the array, from 1 to 256.<\/li>\n<li>Enter the <strong>Drive size<\/strong> of a single drive and pick <strong>GB<\/strong> or <strong>TB<\/strong> as the unit.<\/li>\n<li>For RAID 50 or RAID 60, also set the <strong>Number of groups<\/strong>. Each group must be equally sized, with at least 3 drives per RAID 50 group or 4 per RAID 60 group, and the total drive count must divide evenly by the group count.<\/li>\n<li>Read the results: usable capacity in TB and TiB, raw capacity, array efficiency, fault tolerance, estimated read\/write speed and the minimum drive count for your level.<\/li>\n<\/ol>\n<h2>What Is Usable RAID Capacity?<\/h2>\n<p>Raw capacity is simply every drive added together: 6 drives of 4 TB give 24 TB raw. Usable capacity is what your operating system and file system can actually hold, because every RAID level spends some of that space on redundancy \u2014 parity blocks, mirror copies or both. A 6-drive RAID 5 array stores one drive's worth of parity, so only 20 TB reaches your data. This is why a freshly built array always shows less space than the box labels promised, no matter how it is configured.<\/p>\n<p>The <strong>array efficiency<\/strong> figure expresses the same idea as a percentage: usable divided by raw. RAID 0 and JBOD sit at 100% because nothing is reserved; RAID 1 and RAID 10 settle at 50% because every byte is written twice; RAID 5 approaches 100% as drives are added ((n\u22121)\/n), and RAID 6 trades a second parity drive for better protection, giving (n\u22122)\/n. Compare the efficiency of different levels at your drive count to see exactly what each level of safety costs you in storage.<\/p>\n<p><strong>Fault tolerance<\/strong> counts how many drives can fail without losing data. RAID 5 tolerates one failure, RAID 6 tolerates two, and RAID 10 tolerates one failure per mirror pair (a second failure survives only if it hits a different pair). RAID 50 and RAID 60 tolerate one and two failures <em>per group<\/em>, so total tolerance grows with the group count. RAID 0 and JBOD tolerate none at all: one dead drive takes the whole volume with it. Tolerance is what you buy with the capacity you sacrifice.<\/p>\n<p>The <strong>relative read and write speeds<\/strong> are idealized estimates for sequential workloads, shown as multiples of a single drive's speed. Reads scale with the number of drives in most levels, while parity writes carry a penalty: each RAID 5 write touches about 4 disk operations (the \"4-write penalty\") and each RAID 6 write about 6, which is why RAID 5's write estimate is (n\u22121)\/4. Real speed depends on the controller, cache, stripe size and workload, so treat these numbers as a rough comparison between levels rather than a benchmark.<\/p>\n<h2>RAID Levels at a Glance<\/h2>\n<table>\n<thead>\n<tr>\n<th>Level<\/th>\n<th>Capacity<\/th>\n<th>Fault tolerance<\/th>\n<th>Min. drives<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>RAID 0<\/td>\n<td>\\(n \\cdot s\\)<\/td>\n<td>None<\/td>\n<td>2<\/td>\n<\/tr>\n<tr>\n<td>RAID 1<\/td>\n<td>\\(s\\)<\/td>\n<td>\\(n-1\\) drives<\/td>\n<td>2<\/td>\n<\/tr>\n<tr>\n<td>RAID 5<\/td>\n<td>\\((n-1) \\cdot s\\)<\/td>\n<td>1 drive<\/td>\n<td>3<\/td>\n<\/tr>\n<tr>\n<td>RAID 6<\/td>\n<td>\\((n-2) \\cdot s\\)<\/td>\n<td>2 drives<\/td>\n<td>4<\/td>\n<\/tr>\n<tr>\n<td>RAID 10<\/td>\n<td>\\(\\frac{n}{2} \\cdot s\\)<\/td>\n<td>One per mirror<\/td>\n<td>4 (even)<\/td>\n<\/tr>\n<tr>\n<td>RAID 50<\/td>\n<td>\\((n-g) \\cdot s\\)<\/td>\n<td>One per group<\/td>\n<td>\\(3g\\)<\/td>\n<\/tr>\n<tr>\n<td>RAID 60<\/td>\n<td>\\((n-2g) \\cdot s\\)<\/td>\n<td>Two per group<\/td>\n<td>\\(4g\\)<\/td>\n<\/tr>\n<tr>\n<td>JBOD<\/td>\n<td>\\(n \\cdot s\\)<\/td>\n<td>None<\/td>\n<td>1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>Assumptions, Limitations and Practical Tips<\/h2>\n<ul>\n<li><strong>Identical drives.<\/strong> The calculator assumes all drives are the same size. With mixed sizes, every drive is effectively capped at the smallest one, and usable capacity drops accordingly.<\/li>\n<li><strong>Decimal units.<\/strong> Drive sizes use decimal storage units (1 TB = 1000 GB). Your operating system may report the result in binary TiB, where 1 TiB = 2<sup>40<\/sup> bytes \u2014 that is why 20 TB shows as roughly 18.19 TiB.<\/li>\n<li><strong>File system overhead.<\/strong> Formatting, metadata and the file system's own structures consume a few percent of usable capacity. Leave headroom; do not expect to store a full 20 TB of files on that 20 TB array.<\/li>\n<li><strong>Hot spares.<\/strong> A spare drive reduces the drive count available for data, so subtract it from \\(n\\) if it stands idle and does not participate in the array.<\/li>\n<li><strong>RAID is not a backup.<\/strong> Redundancy protects against drive failure, not against deletion, corruption, ransomware or theft. Keep true backups of anything that matters.<\/li>\n<li><strong>Rebuild risk.<\/strong> With large modern drives, rebuilding a degraded array takes many hours and stresses the surviving drives \u2014 one reason RAID 6 is preferred over RAID 5 for arrays of more than about 6\u20138 large drives.<\/li>\n<li><strong>Securing the array.<\/strong> A storage box often holds your most important data in one place: protect the admin account with a strong password from a <a href=\"https:\/\/wpcalc.com\/en\/web-tools\/password-generator\/\">password generator<\/a>, and give it a predictable address on your network with a planned <a href=\"https:\/\/wpcalc.com\/en\/web-tools\/ip-subnet-calculator\/\">IP subnet<\/a>.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Enter your RAID level, drive count and drive size to find the usable capacity, raw capacity, array efficiency, fault tolerance and estimated speed of your RAID array. Covers RAID 0, 1, 5, 6, 10, 50, 60 and JBOD.<\/p>\n","protected":false},"author":3168,"featured_media":0,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[63],"tags":[102],"class_list":["post-67247","post","type-post","status-publish","format-standard","hentry","category-web-tools","tag-network-tools"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/67247","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/3168"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=67247"}],"version-history":[{"count":1,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/67247\/revisions"}],"predecessor-version":[{"id":67260,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/67247\/revisions\/67260"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=67247"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=67247"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=67247"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}