{ "api_version": "1", "kind": "dse_post", "self": "https://update.dsesecurity.com/api/v1/posts/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/", "item": { "id": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/", "slug": "dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors", "url": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/", "alternate_urls": { "markdown": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors.md", "json": "https://update.dsesecurity.com/api/v1/posts/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/" }, "title": "Budget raw capacity for two-way and three-way mirrors", "summary": "How much raw capacity does a mirrored data-capacity target require?", "format": { "slug": "guide", "name": "Guide" }, "priority": { "slug": "info", "name": "Information" }, "featured": false, "image": { "theme": "continuity-recovery", "label": "Continuity & recovery", "alt": "Paired infrastructure paths converging on a stable recovered service.", "card_url": "https://update.dsesecurity.com/assets/editorial/continuity-recovery-card.webp?v=1.8.20", "hero_url": "https://update.dsesecurity.com/assets/editorial/continuity-recovery-hero.webp?v=1.8.20", "social_url": "https://update.dsesecurity.com/assets/editorial/continuity-recovery-social-v2.jpg?v=1.8.20", "width": 2400, "height": 1350 }, "topics": [ { "slug": "business-continuity", "name": "Business Continuity", "url": "https://update.dsesecurity.com/topic/business-continuity/" }, { "slug": "it", "name": "IT", "url": "https://update.dsesecurity.com/topic/it/" } ], "author": { "name": "DSE Security Editorial Team", "url": "https://update.dsesecurity.com/#editorial-team", "type": "Organization" }, "publisher": { "name": "Detection Systems & Engineering", "url": "https://dsesecurity.com/" }, "published_at": "2026-09-08T18:16:28+00:00", "modified_at": "2026-09-08T18:17:14+00:00", "reviewed_on": "2026-09-08", "reading_minutes": 2, "word_count": 235, "potentially_affected": "Use this review when comparing mirror layouts for a supported cluster.", "dse_recommendation": "Write a capacity worksheet that identifies the copy count, server count, and intended data volume.", "primary_source": { "name": "Fault tolerance and storage efficiency on Azure Local and Windows Server clusters", "url": "https://learn.microsoft.com/en-us/windows-server/storage/storage-spaces/fault-tolerance", "published_on": null, "authority": "Microsoft Learn" }, "publishing_principles": "https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/", "usage_info": "https://update.dsesecurity.com/usage/", "copyright_notice": "Copyright © 2026 Detection Systems & Engineering. All rights reserved.", "content_html": "

Source facts

\n

Storage Spaces Direct mirroring places complete copies on different physical hardware. Two-way mirroring writes two copies and has 50 percent storage efficiency; Microsoft’s example needs at least 2 TB of physical capacity for 1 TB of data and two server fault domains. Three-way mirroring writes three copies, giving 33.3 percent efficiency and requiring at least three server fault domains. Microsoft recommends three-way mirroring when the cluster has more than two servers. Microsoft documentation.

\n

Applicability

\n

Use this review when comparing mirror layouts for a supported cluster. Distinguish raw drive capacity from the usable data target. Review the source’s failure-tolerance discussion and the complete design requirements before selecting a resiliency option.

\n

DSE recommendation

\n

Write a capacity worksheet that identifies the copy count, server count, and intended data volume. Ask the storage owner to review growth, maintenance, and recovery headroom separately from the basic copy calculation. Show the business owner both raw and usable quantities in the proposal. Keep performance and failure requirements alongside cost so the layout is not chosen from capacity efficiency alone.

\n

Verification

\n

Compare the implemented resiliency and reported capacity with the worksheet. Record the actual server and drive inventory, and investigate any unexplained difference in available space. Validate the workload through the approved storage acceptance process. Revisit the calculation when the data target or fault-domain design changes.

\n

Official references

\n

Microsoft Learn: Fault tolerance and storage efficiency on Azure Local and Windows Server clusters. Source reviewed September 8, 2026.

", "content_text": "Source facts\nStorage Spaces Direct mirroring places complete copies on different physical hardware. Two-way mirroring writes two copies and has 50 percent storage efficiency; Microsoft’s example needs at least 2 TB of physical capacity for 1 TB of data and two server fault domains. Three-way mirroring writes three copies, giving 33.3 percent efficiency and requiring at least three server fault domains. Microsoft recommends three-way mirroring when the cluster has more than two servers. Microsoft documentation.\nApplicability\nUse this review when comparing mirror layouts for a supported cluster. Distinguish raw drive capacity from the usable data target. Review the source’s failure-tolerance discussion and the complete design requirements before selecting a resiliency option.\nDSE recommendation\nWrite a capacity worksheet that identifies the copy count, server count, and intended data volume. Ask the storage owner to review growth, maintenance, and recovery headroom separately from the basic copy calculation. Show the business owner both raw and usable quantities in the proposal. Keep performance and failure requirements alongside cost so the layout is not chosen from capacity efficiency alone.\nVerification\nCompare the implemented resiliency and reported capacity with the worksheet. Record the actual server and drive inventory, and investigate any unexplained difference in available space. Validate the workload through the approved storage acceptance process. Revisit the calculation when the data target or fault-domain design changes.\nOfficial references\nMicrosoft Learn: Fault tolerance and storage efficiency on Azure Local and Windows Server clusters. Source reviewed September 8, 2026.", "content_markdown": "## Source facts\n\nStorage Spaces Direct mirroring places complete copies on different physical hardware. Two-way mirroring writes two copies and has 50 percent storage efficiency; Microsoft’s example needs at least 2 TB of physical capacity for 1 TB of data and two server fault domains. Three-way mirroring writes three copies, giving 33.3 percent efficiency and requiring at least three server fault domains. Microsoft recommends three-way mirroring when the cluster has more than two servers. [Microsoft documentation](https://learn.microsoft.com/en-us/windows-server/storage/storage-spaces/fault-tolerance).\n\n## Applicability\n\nUse this review when comparing mirror layouts for a supported cluster. Distinguish raw drive capacity from the usable data target. Review the source’s failure-tolerance discussion and the complete design requirements before selecting a resiliency option.\n\n## DSE recommendation\n\nWrite a capacity worksheet that identifies the copy count, server count, and intended data volume. Ask the storage owner to review growth, maintenance, and recovery headroom separately from the basic copy calculation. Show the business owner both raw and usable quantities in the proposal. Keep performance and failure requirements alongside cost so the layout is not chosen from capacity efficiency alone.\n\n## Verification\n\nCompare the implemented resiliency and reported capacity with the worksheet. Record the actual server and drive inventory, and investigate any unexplained difference in available space. Validate the workload through the approved storage acceptance process. Revisit the calculation when the data target or fault-domain design changes.\n\n## Official references\n\n[Microsoft Learn: Fault tolerance and storage efficiency on Azure Local and Windows Server clusters](https://learn.microsoft.com/en-us/windows-server/storage/storage-spaces/fault-tolerance). Source reviewed September 8, 2026." }, "json_ld": { "@context": "https://schema.org", "@graph": [ { "@type": "Organization", "@id": "https://dsesecurity.com/#organization", "name": "Detection Systems & Engineering", "alternateName": "DSE Security", "url": "https://dsesecurity.com/", "logo": { "@type": "ImageObject", "url": "https://update.dsesecurity.com/assets/dse-logo-20260812.png?v=1.8.20" } }, { "@type": "Organization", "@id": "https://update.dsesecurity.com/#editorial-team", "name": "DSE Security Editorial Team", "url": "https://update.dsesecurity.com/", "parentOrganization": { "@id": "https://dsesecurity.com/#organization" } }, { "@type": "WebSite", "@id": "https://update.dsesecurity.com/#website", "name": "DSE Updates", "alternateName": "DSE Security Knowledge Hub", "url": "https://update.dsesecurity.com/", "inLanguage": "en-US", "publisher": { "@id": "https://dsesecurity.com/#organization" }, "potentialAction": { "@type": "SearchAction", "target": { "@type": "EntryPoint", "urlTemplate": "https://update.dsesecurity.com/?q={search_term_string}" }, "query-input": "required name=search_term_string" } }, { "@type": "WebPage", "@id": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/", "url": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/", "isPartOf": { "@id": "https://update.dsesecurity.com/#website" }, "lastReviewed": "2026-09-08" }, { "@type": "BreadcrumbList", "@id": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/#breadcrumbs", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "DSE Updates", "item": "https://update.dsesecurity.com/" }, { "@type": "ListItem", "position": 2, "name": "Budget raw capacity for two-way and three-way mirrors", "item": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/" } ] }, { "@type": [ "Article", "TechArticle" ], "@id": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/#article", "identifier": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/", "url": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/", "headline": "Budget raw capacity for two-way and three-way mirrors", "description": "How much raw capacity does a mirrored data-capacity target require?", "abstract": "How much raw capacity does a mirrored data-capacity target require?", "articleBody": "Source facts\nStorage Spaces Direct mirroring places complete copies on different physical hardware. Two-way mirroring writes two copies and has 50 percent storage efficiency; Microsoft’s example needs at least 2 TB of physical capacity for 1 TB of data and two server fault domains. Three-way mirroring writes three copies, giving 33.3 percent efficiency and requiring at least three server fault domains. Microsoft recommends three-way mirroring when the cluster has more than two servers. Microsoft documentation.\nApplicability\nUse this review when comparing mirror layouts for a supported cluster. Distinguish raw drive capacity from the usable data target. Review the source’s failure-tolerance discussion and the complete design requirements before selecting a resiliency option.\nDSE recommendation\nWrite a capacity worksheet that identifies the copy count, server count, and intended data volume. Ask the storage owner to review growth, maintenance, and recovery headroom separately from the basic copy calculation. Show the business owner both raw and usable quantities in the proposal. Keep performance and failure requirements alongside cost so the layout is not chosen from capacity efficiency alone.\nVerification\nCompare the implemented resiliency and reported capacity with the worksheet. Record the actual server and drive inventory, and investigate any unexplained difference in available space. Validate the workload through the approved storage acceptance process. Revisit the calculation when the data target or fault-domain design changes.\nOfficial references\nMicrosoft Learn: Fault tolerance and storage efficiency on Azure Local and Windows Server clusters. Source reviewed September 8, 2026.", "datePublished": "2026-09-08T18:16:28+00:00", "dateModified": "2026-09-08T18:17:14+00:00", "mainEntityOfPage": { "@id": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/" }, "inLanguage": "en-US", "isAccessibleForFree": true, "author": { "@type": "Organization", "name": "DSE Security Editorial Team", "url": "https://update.dsesecurity.com/#editorial-team" }, "publisher": { "@id": "https://dsesecurity.com/#organization" }, "image": { "@type": "ImageObject", "@id": "https://update.dsesecurity.com/updates/dse-20260908-043-budget-raw-capacity-for-two-way-and-three-way-mirrors/#primaryimage", "url": "https://update.dsesecurity.com/assets/editorial/continuity-recovery-social-v2.jpg?v=1.8.20", "contentUrl": "https://update.dsesecurity.com/assets/editorial/continuity-recovery-social-v2.jpg?v=1.8.20", "width": 1200, "height": 630, "caption": "Budget raw capacity for two-way and three-way mirrors" }, "articleSection": [ "Business Continuity", "IT" ], "keywords": [ "Business Continuity", "IT", "Guide", "Information priority" ], "genre": "Guide", "about": [ { "@type": "Thing", "name": "Business Continuity", "url": "https://update.dsesecurity.com/topic/business-continuity/" }, { "@type": "Thing", "name": "IT", "url": "https://update.dsesecurity.com/topic/it/" } ], "wordCount": 235, "timeRequired": "PT2M", "publishingPrinciples": "https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/", "usageInfo": "https://update.dsesecurity.com/usage/", "copyrightHolder": { "@id": "https://dsesecurity.com/#organization" }, "copyrightNotice": "Copyright © 2026 Detection Systems & Engineering. All rights reserved.", "citation": { "@type": "CreativeWork", "name": "Fault tolerance and storage efficiency on Azure Local and Windows Server clusters", "url": "https://learn.microsoft.com/en-us/windows-server/storage/storage-spaces/fault-tolerance" } } ] } }