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Storage latency
Latency
<?php
$files = ['file1.txt', 'file2.txt', 'file3.txt'];
$content = "Some contentn";
foreach ($files as $filename) {
$fileHandle = fopen($filename, 'w');
fwrite($fileHandle, $content);
fclose($fileHandle);
}
Let’s write some data to files. The biggest factor here is latency.
Each write requires a roundtrip to the disk and an acknowledgement from the OS.
This isn’t about how many MB/s (bandwidth) your drive can handle, but how low the latency is.
Now imagine doing this for 1,000, 10,000 or even 1,000,000 files!
This write
depends
on
storage
latency](https://image.slidesharecdn.com/20250918cseug-latency-250925112446-3c3d599b/75/Latency-Is-All-That-Matters-Not-Bandwidth-Wido-den-Hollander-26-2048.jpg)
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Latency Is All That Matters, Not Bandwidth - Wido den Hollander
Everyone talks about increasing bandwidth, faster download and upload speeds, NVMe PCIe 5.0 devices pushing gigabytes per se cond. But what if bandwidth isn’t the real bottleneck? Latency is far more important. In this session Wido explores why latency matters more than raw speed and why it matters in CloudStack.
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Latency Is All That Matters, Not Bandwidth - Wido den Hollander
- 1. Latency is allthat matters, not bandwidth September 2025 Public
- 2. 2 • Wido denHollander (1986) • Born and live in the Netherlands • Father of two sons • CTO @ Your.Online • Started my own hosting company in 2003 • Techie in my heart • Open Source & Tech • Apache CloudStack developer and PMC member • Ceph evangelist • IPv6 fanatic Who am I? Wido den Hollander
- 3. 3 Who is Your.Online? Introductionto Your.Online Your.Online is a team of pioneers from all over the world united by the passion of helping businesses succeed online. Our teams of local experts provide highly standardized managed services to high- intent customers to reach their full online potential. We cherish our successful track record in acquiring, developing, and empowering strong local brands to lead their markets 48FTE 1 310 FTE 5 30 FTE 2 200 FTE 5 60 FTE Expand into Market Position 5 50 FTE 1 200 FTE 120 FTE 1 0
- 4. 4 • We runtwo large Apache CloudStack deployments • Yourhosting in the Netherlands • Axarnet in Spain • Deployment at Heart Internet (UK) under development We love CloudStack! Apache CloudStack @ Your.Online Infrastructure at Your.Online
- 5. 5 What is latency? Latency Whocan tell me what latency is?
- 6. 6 Let’s do atest Latency I will ask a couple of you to write the word CloudStack on a piece of paper - Start writing when I say so - Raise your hand when you are done
- 7. 7 Time is theultimate currency Latency Movie: In Time (2011)
- 8. 8 Words per secondvs the time it takes to write a single word Latency A lot of people writing at the same time can you achieve a high Word/s rate (bandwidth) How long (latency) does it take to write a single word?
- 9. 9 Filling out aform Latency Imagine you’re waiting for someone to complete a form. There are 30 people in the room, each working on a form that takes 15 minutes to finish. The total throughput is high: 30×4 = 120 forms per hour. But the latency for any single form is still 15 minutes. Do you want to wait 15 minutes for just one form?
- 10. 10 Bandwidth vs Latency Latency Bandwidthis great! But latency is what matters in most situations
- 11. 11 Why you shouldcare Latency • Latency is what users experience • When you hit ”Play” in Netflix and your show starts • If you click “Add to Cart” and the product is in your shoppingcart • Click “next” to browse through the images of a product and the next image loads • All the things above benefit from a low(er) latency
- 12. 12 What would youchoose? Latency
- 13. 13 What would youchoose? Latency Connection 1 Connection 2 Bandwidth (Mb/s) 1,000 100 Latency (ms) 30 5 What home internet connection would you choose?
- 14. 14 Bandwidth vs Latency Latency Howdoes latency affect your CloudStack deployment in real life?
- 15. 15 The speed oflight Latency Light travels at approximately 299.792.458 m/s in a vacuum. Light could thus travel around the Earth approximately 7,4 times per second at its speed in a vacuum.
- 16. 16 The speed oflight Latency In most standard optical fibers used in datacentres, the speed of light is typically around 200.000 km/s
- 17. 17 Fiber optic cables Latency Lightbounces through a fiber optic cable under an angle, thus the distance travelled is longer A good rule of thumb therefor is that 1km of fiber optic cable leads to 5µs (microseconds) of latency. This includes the refraction and bouncing of the light as it travels down the cable.
- 18. 18 Fiber optic cables Latency Datacentreshouse a large number of cables, which are also widely employed in the connections between various datacentres.
- 19.
- 20.
- 21. 21 Cables, routers andswitches Latency Data centres contain numerous cables, switches, routers, connections, etc. Every link takes time and thus introduces latency SFP+: Converts optical into electrical: Takes time!
- 22. 22 Cables, routers andswitches Latency Each cable, switch, and router contributes extra latency to your IP packets. This added delay causes your application to wait longer for responses. If your application frequently calls external endpoints, this latency becomes more noticeable. Whether it’s APIs, SQL databases, caches, or other services, the greater the latency, the more significant the impact!
- 23. 23 Bandwidth vs Latency Latency Again,how does latency affect your CloudStack deployment in real life?
- 24. 24 Disk I/O latency Latency VMon Local (SATA) SSD storage Latency is x2! Hint: Network! VM on Ceph SSD storage
- 25. 25 Disk I/O latency Latency Yes,local storage is faster. Latency is lower. But it’s also less redundant, so what do you choose? Pick 2, you can’t have all 3!
- 26. 26 Storage latency Latency <?php $files =['file1.txt', 'file2.txt', 'file3.txt']; $content = "Some contentn"; foreach ($files as $filename) { $fileHandle = fopen($filename, 'w'); fwrite($fileHandle, $content); fclose($fileHandle); } Let’s write some data to files. The biggest factor here is latency. Each write requires a roundtrip to the disk and an acknowledgement from the OS. This isn’t about how many MB/s (bandwidth) your drive can handle, but how low the latency is. Now imagine doing this for 1,000, 10,000 or even 1,000,000 files! This write depends on storage latency
- 27. 27 Network latency Latency <?php $redis =new Redis(); $redis->connect($server, 6379); for ($i = 1; $i <= 1000; $i++) { $value = "Value for item $i"; $redis->set("key_$i", $value); } $redis->close(); Let’s write some keys into a Redis database! This write depends on network latency $server Description Latency ::1 Localhost 0,1ms 2001:db8:100::637 8 Server in a different datacenter 1,5ms $server Execution time ::1 0,1*1000 = 100ms 2001:db8:100::6378 1,5*1000 = 1500ms = 1,5s
- 28. 28 Network latency Latency <?php $conn =new mysqli("2001:db8:100::3306", "example_user", "super!secret", "example"); for ($i = 1; $i <= 100; $i++) { $name = "Name_" . $i; $email = "email_" . $i . "@example.com"; $conn->query("INSERT INTO $table_name ('name', 'email') VALUES ('". $name ."', '". $email ."')"); } $conn->close(); Client Storage VM SQL DB Network Network
- 29.
- 30. 30 Cheating is notallowed Latency
- 31. 31 Bandwidth vs Latency Latency Noseriously! How does latency affect your CloudStack deployment in real life?
- 32.
- 33. 33 Nobody ever toldthem latency exists Latency Client/User/Human Application API API API API DB DB DB LATENCY LATENCY LATENCY LATENCY LATENCY LATENCY
- 34. 34 Running it inproduction is so slow Latency Client/User/Human Application API API API API DB DB DB LATENCY LATENCY LATENCY LATENCY LATENCY LATENCY In a place far, far away On Host A On Host B On Hosts X, Y and Z
- 35. 35 There’s even morelatency because we deploy on different hosts Latency Client/User/Human Application API API API API DB DB DB LATENCY LATENCY LATENCY LATENCY LATENCY LATENCY In a place far, far away On Host A On Host B On Hosts X, Y and Z LATENCY LATENCY LATENCY LATENCY
- 36. 36 This is wherethe developer tested the deployment Latency
- 37. 37 Real-world deployments Latency All jokesaside, what can you do in your environment?
- 38. 38 A couple oftips Latency • Deploy VMs which need to talk in the same zone/datacenter/pod • Less latency is better • Use affinity grouping to make sure VMs are located on the same host • Less network latency • Use local storage • Less redundant, lower latency • Avoid writing to storage • If you can, it saves you time
- 39. 39 Remember Latency • Storage ischeap, low latency isn’t • Every layer you add, adds latency • Bandwidth doesn’t matter, latency does • (For most applications)
- 40.
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