--- title: That empty NVMe slot on your NAS isn't decoration — it's... description: Testing SSD caching and app volumes on a Synology DS1621xs+ NAS shows that read-only caching barely helps real-world workloads despite great synthetic... canonical: https://daily.dev/posts/that-empty-nvme-slot-on-your-nas-isn-t-decoration-it-s-the-upgrade-nobody-talks-about-wak1bnayj twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: That empty NVMe slot on your NAS isn't decoration — it's the upgrade nobody talks about | daily.dev og:description: Testing SSD caching and app volumes on a Synology DS1621xs+ NAS shows that read-only caching barely helps real-world workloads despite great synthetic... og:url: https://daily.dev/posts/that-empty-nvme-slot-on-your-nas-isn-t-decoration-it-s-the-upgrade-nobody-talks-about-wak1bnayj og:image: https://api.daily.dev/og/posts/WaK1BNAyJ.png og:image:alt: That empty NVMe slot on your NAS isn't decoration — it's the upgrade nobody talks about og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # That empty NVMe slot on your NAS isn't decoration — it's the upgrade nobody talks about **[XDA Developers](https://daily.dev/sources/xda-developers)** · 5 min read · 0 upvotes · 0 comments ## Summary Testing SSD caching and app volumes on a Synology DS1621xs+ NAS shows that read-only caching barely helps real-world workloads despite great synthetic benchmarks, while a mirrored read-write cache tripled database throughput and cut container start times by nearly 80%. Synology makes dedicating an NVMe drive to its own volume difficult, eating most of the drive's capacity for system partitions unless you use a community compatibility script. TrueNAS and Unraid handle fast-storage tiering more gracefully via L2ARC/special vdevs and the Mover feature respectively. Since most NAS M.2 slots are only PCIe 3.0 x4, buying a Gen5 drive is wasted money; endurance and DRAM matter more than raw speed. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Does enabling SSD read-only cache on a Synology NAS actually speed up real workloads like Docker containers and databases? No, a read-only cache mostly fails to help real workloads. Testing on a Synology DS1621xs+ with DSM 7.4.1 showed a 64% cache hit rate and read latency dropping from 6ms to under 0.25ms in synthetic benchmarks, but container starts, database operations, and file extraction ran the same or slower because those workloads are mostly writes and first-time reads, which a read-only cache never accelerates. _Anyone weighing NAS caching strategies can compare real benchmark results like this on daily.dev._ ### Should I use a read-write cache or a separate volume for Docker and databases on my NAS NVMe slot? A mirrored read-write cache delivered the biggest gains, more than tripling database throughput and cutting container start times by nearly 80% on a Synology DS1621xs+. A dedicated app volume avoids write-back risk entirely but Synology's DSM eats around 10GB per drive for system and swap partitions, making small drives impractical; always use two drives in a read-write mirror since snapshots alone aren't a backup. _Developers self-hosting containers and databases can track NAS storage tuning tactics like this on daily.dev._ ### What PCIe generation do Synology NAS M.2 NVMe slots actually support? Most Synology NAS M.2 slots run at PCIe 3.0 x4, even though Synology doesn't officially publish this spec. Running lspci over SSH on a DS1621xs+ confirmed each M.2 slot gets its own Gen3 x4 link, meaning a Gen5 NVMe drive provides no speed benefit there, so budget should go toward drive endurance and DRAM instead of raw speed. _Self-hosters picking NVMe drives for a NAS upgrade can verify specs like these on daily.dev before buying._ ## Similar posts on daily.dev - [I upgraded my NAS with an SSD cache, then realized more RAM would have solved everything](https://daily.dev/posts/i-upgraded-my-nas-with-an-ssd-cache-then-realized-more-ram-would-have-solved-everything-cfuholvzo) · XDA Developers · 0 upvotes · 0 comments - [I added SSD caching to my NAS and learned why it's not the performance fix everyone claims](https://daily.dev/posts/i-added-ssd-caching-to-my-nas-and-learned-why-it-s-not-the-performance-fix-everyone-claims-ucw0mxdrc) · XDA Developers · 0 upvotes · 0 comments - [Everyone told me SSD caching would fix my NAS, but it fixed absolutely nothing](https://daily.dev/posts/everyone-told-me-ssd-caching-would-fix-my-nas-but-it-fixed-absolutely-nothing-maoiqxoou) · XDA Developers · 0 upvotes · 0 comments - [The 10 Ways NAS is Getting Enshitified](https://daily.dev/posts/the-10-ways-nas-is-getting-enshitified-vqvgmqnm0) · Hacker News · 0 upvotes · 0 comments - [I dusted off an old SSD and it became my best storage upgrade this year](https://daily.dev/posts/i-dusted-off-an-old-ssd-and-it-became-my-best-storage-upgrade-this-year-wwssmxumw) · XDA Developers · 0 upvotes · 0 comments --- Tags: [#truenas](https://daily.dev/tags/truenas) [View this post on daily.dev](https://daily.dev/posts/that-empty-nvme-slot-on-your-nas-isn-t-decoration-it-s-the-upgrade-nobody-talks-about-wak1bnayj) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"That empty NVMe slot on your NAS isn't decoration — it's the upgrade nobody talks about","url":"https://daily.dev/posts/that-empty-nvme-slot-on-your-nas-isn-t-decoration-it-s-the-upgrade-nobody-talks-about-wak1bnayj","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/that-empty-nvme-slot-on-your-nas-isn-t-decoration-it-s-the-upgrade-nobody-talks-about-wak1bnayj"},"datePublished":"2026-10-01T14:03:28.953Z","dateModified":"2026-10-01T14:08:18.886Z","description":"Testing SSD caching and app volumes on a Synology DS1621xs+ NAS shows that read-only caching barely helps real-world workloads despite great synthetic...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/99f5c97d536eb832572468f0002192e8?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/99f5c97d536eb832572468f0002192e8?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"XDA Developers","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"XDA Developers","logo":"https://media.daily.dev/image/upload/s--kCg6yyAP--/f_auto,q_auto/v1774964407/logos/xda-developers?_a=BAMAMiWQ0","url":"https://daily.dev/sources/xda-developers"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/that-empty-nvme-slot-on-your-nas-isn-t-decoration-it-s-the-upgrade-nobody-talks-about-wak1bnayj","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"truenas","timeRequired":"PT5M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"XDA Developers","item":"https://daily.dev/sources/xda-developers"},{"@type":"ListItem","position":3,"name":"That empty NVMe slot on your NAS isn't decoration — it's the upgrade nobody talks about"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/that-empty-nvme-slot-on-your-nas-isn-t-decoration-it-s-the-upgrade-nobody-talks-about-wak1bnayj#faq","mainEntity":[{"@type":"Question","name":"Does enabling SSD read-only cache on a Synology NAS actually speed up real workloads like Docker containers and databases?","acceptedAnswer":{"@type":"Answer","text":"No, a read-only cache mostly fails to help real workloads. 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