{"id":22265,"date":"2026-09-18T16:45:05","date_gmt":"2026-09-18T08:45:05","guid":{"rendered":"https:\/\/www.luleey.com\/?p=22265"},"modified":"2026-09-16T16:48:45","modified_gmt":"2026-09-16T08:48:45","slug":"10gbe-slow-file-transfers-test-with-iperf3-first","status":"publish","type":"post","link":"https:\/\/www.luleey.com\/ja\/10gbe-slow-file-transfers-test-with-iperf3-first\/","title":{"rendered":"10GbE\u3067\u30d5\u30a1\u30a4\u30eb\u8ee2\u9001\u304c\u9045\u3044\uff1f\u3000\u307e\u305a\u306fiperf3\u3067\u30c6\u30b9\u30c8\u3057\u3066\u307f\u307e\u3057\u3087\u3046"},"content":{"rendered":"\n<p class=\"wp-block-wd-paragraph wd-9ae35827\">Troubleshooting <strong><a style=\"color: #FF6A00;\" target=\"_blank\" href=\"https:\/\/www.luleey.com\/ja\/tag\/10gbe\/\" title=\"View all posts in 10GbE\">10GbE<\/a> slow file transfers<\/strong> starts with separating three numbers: the port\u2019s link speed, the throughput between two computers, and the speed of the file copy itself.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-88f36a4b\">A 10G link indicator confirms a link rate\u2014not a guaranteed <a style=\"color: #FF6A00;\" target=\"_blank\" href=\"https:\/\/www.luleey.com\/ja\/tag\/nas\/\" title=\"View all posts in NAS\">NAS<\/a> transfer speed. Before replacing an SFP+ module, run a local network test between the same endpoints used for the slow copy. Then compare the results with a controlled file transfer.<\/p>\n\n\n\n<div class=\"wp-block-wd-image wd-block-image wd-ef87a004\"><img loading=\"lazy\" decoding=\"async\" width=\"1000\" height=\"1000\" class=\"wp-image-22266\" src=\"https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-slow-file-transfers-hero.png\" alt=\"\" title=\"\" srcset=\"https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-slow-file-transfers-hero.png 1000w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-slow-file-transfers-hero-800x800.png 800w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-slow-file-transfers-hero-400x400.png 400w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-slow-file-transfers-hero-768x768.png 768w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-slow-file-transfers-hero-12x12.png 12w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-slow-file-transfers-hero-150x150.png 150w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><\/div>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-d3c037ff\">10GbE Slow File Transfers: Check the Units First<\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-ed9e4e3b\">Network speeds are usually shown in <strong>Gbps<\/strong> or <strong>Mbits\/sec<\/strong>. File-copy tools commonly show <strong>MB\/s<\/strong> or <strong>MiB\/s<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-e425c175\">Using decimal units:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>10 Gbps \u00f7 8 = 1.25 GB\/s before protocol overhead.<\/li>\n\n\n\n<li>100 MB\/s \u00d7 8 = 800 Mbps.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-04b1fb5f\">Neither number is a diagnosis. A 100 MB\/s copy could be constrained by a slower network segment, storage or the application. Also check whether the copy tool uses MiB\/s rather than decimal MB\/s.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-c71a067e\">1. Confirm Which Network Path You Are Testing<\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-a64a045f\">Write down the path from client to NAS, including every intermediate switch, converter and uplink. Check the actual operating rate at each relevant interface\u2014not just the adapter\u2019s advertised capability.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-afcb9abc\">Use the NAS address assigned to the intended wired interface. A hostname may lead to a different interface. Confirm that the transfer is not taking Wi-Fi, a VPN, a management port or an unexpected routed path.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-95b6a2e2\">For a copper SFP+ module, the host-facing electrical rate and RJ45 negotiation can differ. A supported rate-adaptive combination may show 10G at the host while its copper peer operates at 2.5G. See LuLeey\u2019s guide to <a href=\"https:\/\/www.luleey.com\/can-a-10g-sfp-port-connect-to-2-5g-rj45\/\">connecting a 10G SFP+ port to 2.5G RJ45<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-0ae9312f\">Physical fit, host SerDes mode, negotiated rates and usable throughput are separate checks. Record the exact host and module models, host chipset\/PHY, firmware, driver, port settings and module coding before drawing compatibility conclusions. A cage marked SFP+ does not settle them.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-fbbcd6e7\">2. Run a Local Network Test Without Copying Files<\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-ff191b6f\">Use two authorized machines on the affected path. Ideally, run the server on the NAS itself; a different server only tests the path to that server. Do not test against <code>localhost<\/code> or an Internet speed-test site.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-e847a619\">These commands assume a trusted, compatible <a style=\"color: #FF6A00;\" target=\"_blank\" href=\"https:\/\/www.luleey.com\/ja\/tag\/iperf3\/\" title=\"View all posts in iperf3\">iperf3<\/a> installation. ESnet does not officially support iperf3 on Windows; verify any Windows build separately, or use a supported platform. A VM or container introduces another path to document. See the <a href=\"https:\/\/software.es.net\/iperf\/faq.html\" target=\"_blank\" rel=\"noopener\">ESnet compatibility FAQ<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-6ddbeef6\">For this example, the server\u2019s LAN address is <code>192.168.10.20<\/code>. Replace it with your actual address. Test during a quiet period: throughput tests can congest the network. Permit TCP 5201 only between the test machines; do not expose the server to the Internet.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-356f3575\">On the server:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>iperf3 -s -B 192.168.10.20<\/code><\/pre>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-308b1fc2\">On the client, run these separately:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>iperf3 -c 192.168.10.20 -t 30\niperf3 -c 192.168.10.20 -t 30 -R<\/code><\/pre>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-3c811427\">The first sends client \u2192 server. <code>-R<\/code> sends server \u2192 client. These are consecutive tests, not simultaneous bidirectional traffic.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-afbca652\">If a single stream is slow, compare four streams:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>iperf3 -c 192.168.10.20 -t 30 -P 4\niperf3 -c 192.168.10.20 -t 30 -P 4 -R<\/code><\/pre>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-ddf37e86\">Save the final receiver summary; for parallel tests, use the aggregate <code>[SUM]<\/code> result. Record CPU use, retransmissions where reported, and interface-counter changes. Stop the server with Ctrl+C afterward. Command behavior is documented in the <a href=\"https:\/\/software.es.net\/iperf\/invoking.html\" target=\"_blank\" rel=\"noopener\">official iperf3 manual<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-957c9c21\">Ordinary tests generate traffic without reading your source file or writing a destination file. They still depend on the endpoints, software and network path\u2014not just the cable.<\/p>\n\n\n\n<div class=\"wp-block-wd-image wd-block-image wd-6c08efeb\"><img loading=\"lazy\" decoding=\"async\" width=\"1000\" height=\"1000\" class=\"wp-image-22267\" src=\"https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-iperf3-test-directions.png\" alt=\"\" title=\"\" srcset=\"https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-iperf3-test-directions.png 1000w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-iperf3-test-directions-800x800.png 800w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-iperf3-test-directions-400x400.png 400w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-iperf3-test-directions-768x768.png 768w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-iperf3-test-directions-12x12.png 12w, https:\/\/www.luleey.com\/wp-content\/uploads\/2026\/09\/10gbe-iperf3-test-directions-150x150.png 150w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><\/div>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-39602eda\">3. Let the Results Choose the Next Check<\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-7e17c17d\">The patterns below are diagnostic clues, not universal pass\/fail thresholds.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>What you observe<\/th><th>Useful next step<\/th><\/tr><\/thead><tbody><tr><td>TCP tests are much faster than the file copy in the same direction<\/td><td>Investigate storage and file-sharing workload first; confirm both tests use the same path.<\/td><\/tr><tr><td>Both directions are slow<\/td><td>Recheck every link rate, endpoint CPU, NIC\/driver and intermediate device.<\/td><\/tr><tr><td>Only one direction is slow<\/td><td>Compare sending and receiving endpoints, errors, drops and any rate-adaptation boundary.<\/td><\/tr><tr><td>Four streams substantially outperform one<\/td><td>Investigate per-flow or endpoint limits; do not treat aggregate speed as a single-file guarantee.<\/td><\/tr><tr><td>Performance worsens as errors or link events rise<\/td><td>Isolate the affected physical segment and repeat under the same conditions.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-87334223\">Record the iperf3 version at both ends. Older advice describing all iperf3 tests as single-threaded is version-dependent: ESnet documents one thread per stream from version 3.16 onward. That does not mean four streams will always help.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-faa51487\">Do not change MTU, flow control, drivers and modules together. Keep a known-working baseline, make one justified change, and repeat the same test.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-a38df9d0\">4. Compare a Controlled File Copy<\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-f56bd73c\">If TCP performance is good, copy one large, ordinary file into a dedicated test folder without overwriting existing data. Check both directions. Then compare a folder of small files.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-af5a864c\">Watch source read speed, destination write speed and CPU use. A fast opening burst followed by a slowdown can reflect exhausted caches. Many small files add repeated metadata operations. <a style=\"color: #FF6A00;\" target=\"_blank\" href=\"https:\/\/www.luleey.com\/ja\/tag\/smb\/\" title=\"View all posts in SMB\">SMB<\/a> signing and encryption can add CPU work; keep required security protections enabled.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-ce5eaff7\"><a href=\"https:\/\/learn.microsoft.com\/en-us\/troubleshoot\/windows-server\/networking\/slow-smb-file-transfer\" target=\"_blank\" rel=\"noopener\">Microsoft\u2019s SMB troubleshooting guidance<\/a> explains these storage, caching and workload effects. They are reasons to investigate the file-copy path\u2014not proof that your particular NAS has a disk fault.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-71709a5a\">For example, a <strong>hypothetical<\/strong> result of 9 Gbps in a same-direction TCP test and 220 MB\/s in a file copy shifts the next check toward storage and file sharing. It does not certify every network condition or identify one failed component.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-9b980903\">5. Investigate Modules When the Evidence Points There<\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-27eebf77\">If network tests are also poor, compare interface counters before and after each run. Increasing CRC\/FCS errors justify checking the relevant physical link; drops without CRC errors can have other causes, including congestion. A TCP retransmission count alone does not identify a bad module.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-1946c4d9\">For copper links, substitute a known-good cable within the selected module\u2019s documented reach. For optical links, verify the fiber type, matched transceivers, connector condition and model-specific receive-power limits. Inspect and clean with appropriate tools; never look into a fiber or optical port.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-5bc4d287\">Also check host power and cooling requirements. If the interface repeatedly goes down and up, follow the separate <a href=\"https:\/\/www.luleey.com\/10gbase-t-sfp-link-flapping-causes-and-fixes\/\">10GBASE-T SFP+ link-flapping checklist<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-6913cbb9\">Swap one component at a time. Repeat in the original setup if safe: a result that follows a particular component is more useful than a one-off improvement after several changes.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-baf52fff\">Before Buying a Different Module<\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-8a72d716\">LuLeey\u2019s <a href=\"https:\/\/www.luleey.com\/solutions\/10g-homelab-upgrade\/\">10G HomeLab Upgrade Solution<\/a> covers copper, DAC\/AOC and optical connection options. Its <a href=\"https:\/\/www.luleey.com\/product\/10gbase-t-sfp-to-rj45-copper-module-30m-80m-100m\/\">10GBASE-T SFP+ to RJ45 module page<\/a> offers multiple variants; confirm the selected hardware, supported modes and reach against your actual setup. Do not assume every option behaves identically.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-f4bddfd3\">For useful compatibility advice, send LuLeey:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Both endpoint models, host chipset\/PHY, firmware and drivers<\/li>\n\n\n\n<li>Module variant, coding, host mode and port settings<\/li>\n\n\n\n<li>Cable type, length and complete connection path<\/li>\n\n\n\n<li>Observed rates on both sides of any converter or copper module<\/li>\n\n\n\n<li>Forward\/reverse TCP results, CPU use and counter changes<\/li>\n\n\n\n<li>File-copy direction, speed, workload and storage observations<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-3d32eb59\"><strong>Start with the comparison, not the replacement:<\/strong> confirm the path, test TCP in both directions, then compare file copies. This tells you where the next test belongs.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u89b3\u5bdf\u7d50\u679c\u3000\u4eca\u5f8c\u306e\u6709\u52b9\u306a\u5bfe\u5fdc\u7b56\u3000TCP\u30c6\u30b9\u30c8\u306f\u3001\u540c\u3058\u65b9\u5411\u3067\u306e\u30d5\u30a1\u30a4\u30eb\u30b3\u30d4\u30fc\u3088\u308a\u3082\u306f\u308b\u304b\u306b\u9ad8\u901f\u3067\u3042\u308b\u3000\u8abf\u67fb\u3059\u308b<\/p>","protected":false},"author":1,"featured_media":22266,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1077],"tags":[1514,1655,1653,1654,1658,1656,1657],"class_list":["post-22265","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-problem-cases","tag-homelab","tag-10gbe","tag-iperf3","tag-nas","tag-network-performance","tag-sfp-troubleshooting-2","tag-smb"],"_links":{"self":[{"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/posts\/22265","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/comments?post=22265"}],"version-history":[{"count":1,"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/posts\/22265\/revisions"}],"predecessor-version":[{"id":22290,"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/posts\/22265\/revisions\/22290"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/media\/22266"}],"wp:attachment":[{"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/media?parent=22265"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/categories?post=22265"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.luleey.com\/ja\/wp-json\/wp\/v2\/tags?post=22265"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}