• ## Bcache against Flashcache for Ceph Object Storage

Fast SSDs are getting cheaper every year, but they are still smaller and more expensive than traditional HDD drives. But HDDs have much higher latency and are easily saturated. However, we want to achieve low latency for the storage system, and a high capacity too. There’s a well-known practice of optimizing performance for big and slow devices — caching. As most of the data on a disk is not accessed most of the time but some percentage of it is accessed frequently, we can achieve a higher quality of service by using a small cache.

Server hardware and operating systems have a lot of caches working on different levels. Linux has a page cache for block devices, a dirent cache and an inode cache on the filesystem layer. Disks have their own cache inside. CPUs have caches. So, why not add one more persistent cache layer for a slow disk?
• ## Powershell way to exclude folder from Defender list

• Tutorial
To exclude some folder from the defender list can be used cmdlet Set-MpPreference
Manly, now you can stop reading, go to the PowerShell and update excludes:)
But if you are want to see how to perform this in more detail — welcome under the habrcut.

UPD: Added a script to add selected folder to excluded Defender locations (at the end of the post)
• ## Managing hundreds of servers for load testing: autoscaling, custom monitoring, DevOps culture

In the previous article, I talked about our load testing infrastructure. On average, we use about 100 servers to create a load, about 150 servers to run our service. All these servers need to be created, configured, started, deleted. To do this, we use the same tools as in the production environment to reduce the amount of manual work:

• Terraform scripts for creating and deleting a test environment;
• Ansible scripts for configuring, updating, starting servers;
• In-house Python scripts for dynamic scaling, depending on the load.

Thanks to the Terraform and Ansible scripts, all operations ranging from creating instances to starting servers are performed with only six commands:

#launch the required instances in the AWS console
ansible-playbook deploy-config.yml #update servers versions
ansible-playbook start-application.yml #start our app on these servers
ansible-playbook update-test-scenario.yml --ask-vault-pass #update the JMeter test scenario if it was changed
infrastructure-aws-cluster/jmeter_clients:~# terraform apply #create JMeter servers for creating the load
playbook start-jmeter-server-cluster.yml #start the JMeter cluster
ansible-playbook start-stress-test.yml #start the test


• ## Ansible: CoreOS to CentOS, 18 months long journey

There was a custom configuration management solution.

I would like to share the story about a project. The project used to use a custom configuration management solution. Migration lasted 18 months. You can ask me 'Why?'. There are some answers below about changing processes, agreements and workflows.

• ## How to test Ansible and don't go nuts

It is the translation of my speech at DevOps-40 2020-03-18:

After the second commit, each code becomes legacy. It happens because the original ideas do not meet actual requirements for the system. It is not bad or good thing. It is the nature of infrastructure & agreements between people. Refactoring should align requirements & actual state. Let me call it Infrastructure as Code refactoring.

• ## Porting packages to buildroot using the Zabbix example

• Tutorial

## The basics of porting

Originally, Buildroot offers a limited number of packages. It makes sense — there is everything you need, but any other packages can be added.

To add a package, create 2 description files, an optional checksum file, and add a link to the package in the general package list. There are hooks at different stages of the build. At the same time, Buildroot can recognize the needed type of packages:

• ## When the COVID-19 pandemic will end

Dear all,

I am the head of Data Science at British Transport Police, and one of our department tasks is to efficiently allocate staff, depending on the crime rates, which correlate to passenger flow. As you understand, the passenger flow will undertake significant change as soon as the Government decides to cancel quarantine or stop some limitations. The question naturally arises: when will the pandemic end and how to prepare for a return to normal life.

AdBlock has stolen the banner, but banners are not teeth — they will be back

• ## Scientists Turn a Quantum Computer into a Time Machine — At least, for a Second…

Scientists said they were able to return the state of a quantum computer a fraction of a second into the past, according to a university press release. The researchers, who are from the Moscow Institute of Physics and Technology, along with colleagues from the U.S. and Switzerland, also calculated the probability that an electron in empty interstellar space will spontaneously travel back into its recent past. The study came out recently in Scientific Reports.
“This is one in a series of papers on the possibility of violating the second law of thermodynamics. That law is closely related to the notion of the arrow of time that posits the one-way direction of time: from the past to the future,” commented the study’s lead author Gordey Lesovik, who heads the Laboratory of the Physics of Quantum Information Technology at MIPT.

While the researchers don’t expect you to take a trip back to the high school prom just yet, they added that the time reversal algorithm could prove useful for making quantum computers more precise.

“Our algorithm could be updated and used to test programs written for quantum computers and eliminate noise and errors,” Lebedev explained.

The researchers said that the work builds on some earlier work that recently garnered headlines.

“We began by describing a so-called local perpetual motion machine of the second kind. Then, in December, we published a paper that discusses the violation of the second law via a device called a Maxwell’s demon,” Lesovik said. “The most recent paper approaches the same problem from a third angle: We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time.”
• ## Simple and free video conferencing

Due to a rapid increase in remote work, we have decided to offer video conferencing. Like most of our services, it is free of charge. It is built on a reliable open-source solution, it is mostly based on WebRTC, which allows communicating in the browser by just clicking on a link. Below we’ll tell you more about its features and some of the problems we’ve run into.

• ## Safe-enough linux server, a quick security tuning

###### The case: You fire up a professionally prepared Linux image at a cloud platform provider (Amazon, DO, Google, Azure, etc.) and it will run a kind of production level service moderately exposed to hacking attacks (non-targeted, non-advanced threats).

What would be the standard quick security related tuning to configure before you install the meat?

release: 2005, Ubuntu + CentOS (supposed to work with Amazon Linux, Fedora, Debian, RHEL as well)

• ## Windows Native Applications and Acronis Active Restore

• Translation
We continue telling you about our cooperation with Innopolis University guys to develop Active Restore technology. It will allow users to start working as soon as possible after a failure. Today, we will talk about Native Windows applications, including details on their development and launch. Under the cut, you will find some information about our project, and a hands-on guide on developing native apps.

# Top-5 HTTP Security Headers in 2020

• ## The World’s Top 12 Quantum Computing Research Universities

In just a few years, quantum computing and quantum information theory has gone from a fringe subject offered in small classes at odd hours in the corner of the physics building annex to a full complement of classes in well-funded programs being held at quantum centers and institutes at leading universities.

The question now for many would-be quantum computer students is not, “Are there universities that even offer classes in quantum computing,” but, rather, “Which universities are leaders at quantum computing research.”

We’ll look at some of the best right now:

#### The Institute for Quantum Computing — University of Waterloo

The University of Waterloo can proudly declare that, while many universities avoided offering quantum computing classes like cat adoption agencies avoided adoption applications from the Schrodinger family, this Canadian university went all in.

And it paid off.
• ## Service for Active Restore or the Story of an Industrial Project at Innopolis

• Translation
Hello, Habr! My name is Roman. Today I would like to share a story of how we at Innopolis University developed a test stand and a service for Acronis Active Restore system, which will soon become part of the company’s product range. Those interested to know how the University builds its relationship with industrial partners are welcome to click the «Read More» button.

## Intro

Like I said earlier in previos articles, Buildroot is a great system for embedded Linux development. But sometimes strange things can happen.

Once upon a workday, I got the following task: add printing system in firmware (Kraftway terminal Linux next generation). Ok, so I had to add cups + cups filter and to build firmware. I set a postscript-printer and got an error "Filter failed". Trivial tasks turned into serious work.

In this article, I wrote my own way of solving this problem. It may be useful for other developers and IT-specialist and, also, for a deeper understanding of the Buildroot.

If you are a Buildroot beginner, I recommend reading my previous articles.

## Update 1 may 2020

Revisioned versions of this patches applied to master.

• ## Deploying Tarantool Cartridge applications with zero effort (Part 2)

• Tutorial

We have recently talked about how to deploy a Tarantool Cartridge application. However, an application's life doesn't end with deployment, so today we will update our application and figure out how to manage topology, sharding, and authorization, and change the role configuration.

• ## Active Restore: Can we Recover Faster? Much Faster?

• Translation
Backing up valuable data is a proven practice, but what if we need to continue work immediately after a natural disaster or other disruptive events, and every minute is important? Our team at Acronis decided to see how quickly we can start an operating system. This is our first post from the Active Restore series. Today I will tell you how we launched our project with Innopolis University, which solutions were studied, and what we are working on today. All the details are under the Cut.

• ## This is how you deal with route leaks

That, we must say, is the unique story so far.

Here’s the beginning: for approximately an hour, starting at 19:28 UTC on April 1, 2020, the largest Russian ISP — Rostelecom (AS12389) — was announcing prefixes belonging to prominent internet players: Akamai, Cloudflare, Hetzner, Digital Ocean, Amazon AWS, and other famous names.

Before the issue was resolved, paths between the largest cloud networks were somewhat disrupted — the Internet blinked. The route leak was distributed quite well through Rascom (AS20764), then Cogent (AS174) and in a couple of minutes through Level3 (AS3356) to the world. The issue suddenly became bad enough that it saturated the route decision-making process for a few Tier-1 ISPs.

It looked like this:

With that:

## СOVID-19 and Internet

Recent events caused by coronavirus spread have highlighted quite a few problem areas in society, economics, technology… And it’s not only about the panic, which is inevitable and will come back with any following global issue. But it is really about the consequences: crowded hospitals, empty shelves in supermarkets, people having to stay at home and use up the Internet which turns out to not be enough for everyone who’s going through the hard days and nights of #stayathome.