--- title: I upgraded my NAS to 10 Gigabit and immediately... description: Upgrading a Synology DS1621xs+ NAS to 10 GbE networking revealed that the real bottleneck was the storage array, not the network. Two 20TB drives in RAID 1... canonical: https://daily.dev/posts/i-upgraded-my-nas-to-10-gigabit-and-immediately-discovered-the-bottleneck-nobody-warns-you-about-wxz34mogx twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: I upgraded my NAS to 10 Gigabit and immediately discovered the bottleneck nobody warns you about | daily.dev og:description: Upgrading a Synology DS1621xs+ NAS to 10 GbE networking revealed that the real bottleneck was the storage array, not the network. Two 20TB drives in RAID 1... og:url: https://daily.dev/posts/i-upgraded-my-nas-to-10-gigabit-and-immediately-discovered-the-bottleneck-nobody-warns-you-about-wxz34mogx og:image: https://api.daily.dev/og/posts/WxZ34MOgX.png og:image:alt: I upgraded my NAS to 10 Gigabit and immediately discovered the bottleneck nobody warns you 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. # I upgraded my NAS to 10 Gigabit and immediately discovered the bottleneck nobody warns you about **[XDA Developers](https://daily.dev/sources/xda-developers)** · 5 min read · 0 upvotes · 0 comments ## Summary Upgrading a Synology DS1621xs+ NAS to 10 GbE networking revealed that the real bottleneck was the storage array, not the network. Two 20TB drives in RAID 1 (SHR) cap sequential writes at ~290 MB/s — barely 20% of 10 GbE capacity. RAID 1 doesn't double read speeds for single clients; Linux only reads from one mirror member at a time. SMB adds another constraint: single-file copies use one TCP stream on one CPU core, limiting throughput further. SMB Multichannel only arrived in DSM 7.2. Encryption compounds the problem — low-power NAS CPUs can drop read throughput below 100 MB/s with AES-CMAC enabled. Saturating a 10 GbE link would require six HDDs in RAID 5/SHR or SATA SSDs, not a two-drive mirror. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Does RAID 1 mirroring double read speed on a NAS like Synology's SHR? No, a single sequential read comes from only one mirror member, not both drives at once. Linux kernel developers have documented this behavior for two decades. Read balancing across mirror drives only kicks in when multiple clients pull data simultaneously; a single large file copy is served by just one drive, capping throughput around 290 MB/s on two 20TB drives in SHR. _Anyone planning NAS redundancy should weigh RAID1's real-world read limits before assuming mirrors speed things up, a topic worth following on daily.dev._ ### When did SMB Multichannel support arrive in Synology DSM? SMB Multichannel arrived in DSM version 7.2. Without it, a single file copy over SMB is handled by one TCP stream on a single CPU core, meaning transfer speed is limited to single-threaded performance per connection regardless of how fast the underlying network link is. _Readers troubleshooting slow NAS transfers over SMB can keep tabs on protocol changes like this via daily.dev._ ### How much does AES-CMAC encryption slow down NAS read throughput on a low-power CPU? Enabling AES-CMAC signing for data-at-rest encryption drags read throughput below 100 MB/s on a low-power quad-core Xeon D-1527 NAS CPU, even when the CPU is not otherwise the bottleneck for unencrypted transfers. This makes a fast 10 GbE network link largely irrelevant once encryption is turned on for that class of hardware. _Anyone deciding whether to enable NAS encryption can factor in throughput trade-offs like this through daily.dev._ ## Similar posts on daily.dev - [I thought my NAS drives were the bottleneck, but 2.5GbE networking proved me wrong](https://daily.dev/posts/i-thought-my-nas-drives-were-the-bottleneck-but-2-5gbe-networking-proved-me-wrong-tsueyvktp) · XDA Developers · 0 upvotes · 0 comments - [I built my NAS from an old gaming PC, and nothing released since has justified replacing it](https://daily.dev/posts/i-built-my-nas-from-an-old-gaming-pc-and-nothing-released-since-has-justified-replacing-it-fvmm85agq) · XDA Developers · 0 upvotes · 0 comments - [Debugging my new network, when 10 Gigabit Ethernet Runs at 300 Megabits](https://daily.dev/posts/debugging-my-new-network-when-10-gigabit-ethernet-runs-at-300-megabits-intohpmzt) · Scott Hanselman · 3 upvotes · 2 comments - [10GbE networking is a trap, unless you're using it for this one thing](https://daily.dev/posts/10gbe-networking-is-a-trap-unless-you-re-using-it-for-this-one-thing-c8jb5uoph) · XDA Developers · 1 upvotes · 1 comments - [Making Davinci Resolve Faster: Speeding Up SMB Reads From MacOS to Linux](https://daily.dev/posts/making-davinci-resolve-faster-speeding-up-smb-reads-from-macos-to-linux-s3o8qngpa) · scottstuff.net · 0 upvotes · 0 comments --- Tags: [#storage](https://daily.dev/tags/storage), [#networking](https://daily.dev/tags/networking) [View this post on daily.dev](https://daily.dev/posts/i-upgraded-my-nas-to-10-gigabit-and-immediately-discovered-the-bottleneck-nobody-warns-you-about-wxz34mogx) ```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":"I upgraded my NAS to 10 Gigabit and immediately discovered the bottleneck nobody warns you about","url":"https://daily.dev/posts/i-upgraded-my-nas-to-10-gigabit-and-immediately-discovered-the-bottleneck-nobody-warns-you-about-wxz34mogx","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/i-upgraded-my-nas-to-10-gigabit-and-immediately-discovered-the-bottleneck-nobody-warns-you-about-wxz34mogx"},"datePublished":"2026-08-07T21:04:14.298Z","dateModified":"2026-09-13T19:31:18.702Z","description":"Upgrading a Synology DS1621xs+ NAS to 10 GbE networking revealed that the real bottleneck was the storage array, not the network. 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