Uncategorized – Page 34

OpenWRT and Android USB Tethering For Backhaul

When traveling, I use Wi-Fi tethering with a smartphone a lot to keep my notebook and other devices connected. When staying at a place for more than just a day or two, however, I prefer a somewhat more sophisticated setup with a Linksys router running OpenWRT.

No, this is not just a fancy but often a must. For one thing, a dedicated router with good antennas results in a much better Wi-Fi range on both the 2.4 and 5 GHz bands and both bands can be used simultaneously. Also, I can make use of sophisticated features such as traffic shaping to keep round trip delays to a minimum. This is particularly important when uploading large amounts of data while doing attending conference calls.

Reaching 1 Gbit/s With a 160 MHz Wi-Fi Channel

This is again one of the moments where I broke through a boundary that existed for years: Reaching 1 Gbit/s Ethernet line speed over Wi-Fi.

In the past, I’ve come close to around 800 Mbit/s, but that was only for a short time, as radar detection frequently moved my 80 MHz channel to the lower part of the 5 GHz band. Here, transmit power is much more limited then higher up in the band, so in practice, I can reach around 500 Mbit/s today. While my previous 6 year old notebook was limited to 80 MHz channels, my new Lenovo X13 comes with an Intel AX-200 Wi-Fi card that supports 802.11ac and 11ax with 160 MHz channels. Incidentally, my Wi-Fi Access Point, a Fritzbox 7590 also supports 160 MHz channels, so it was time to see how fast things could get with such a channel bandwidth.

Wi-Fi Radar Detection in Practice

I’m a heavy user of the 5 GHz band at home for Wi-Fi, as I’m not inclined to drill half a dozen of holes through several rooms to get ‘the Internet’ and high speed connectivity from my local servers (i.e. ‘the private cloud’) to my workspace. My biggest enemy: The required radar detection and subsequent downgrade of the Wi-Fi channel to the lowest 80 MHz of the band.

So what’s the problem with using the lower part of the 5 GHz band? In practice, whenever radar is supposedly detected, my link rate drops from almost 800 Mbit/s to 500 Mbit/s for a while, as transmit power is limited in that part. Also I’m limited to an 80 MHz channel.

LED Fatigue

Here’s an interesting phenomenon I came across recently on a router that was in constant operation for well over two years: The white LEDs that were constantly switched-on did not age very gracefully.

Real World Performance – Part 5 – Fast SATA to USB Adapters

In episode 4, I was able to push my LUKS encrypted disk to disk data transfer rate to around 300 MB/s which already saves a lot of time over my previous methods for migrating a lot of data from an old to a new SSD. However, I wasn’t fully satisfied because even older SATA SSDs can often be read at the full 6 Gbit/s SATA speed, i.e. at around 500 MB/s. The bottleneck in my case thus might have been the the 5 GBit/s SATA to USB 3 adapters. However, there are now 10 Gbit/s SATA to USB 3.1 Gen 2 adapters available so I bought one of those for around 20 euros to see if I could further push the limit.

Real World Performance – Part 4 – partclone

Another thing I have to do every now and then is to clone a partition to a new drive, e.g. for backup purposes or when upgrading. Depending on the amount of data to transfer, this can be quite a lengthy procedure. Copying 2 TB worth of data from one drive to another, for example, can take quite some time. rsync is a great tool to do this but it seems to be rather slow in practice. So far, I can’t get more than 120 MB/s out of it, even if both source and destination are local SSDs. Furthermore, when copying very small files, the transfer rate plunges into a back hole. So in practice with my mix of data, the whole operation usually takes half a day at least. So perhaps there’s a better way? How about partclone?

Real World Performance – Part 3 – Another NVMe

In the first part of this “Real World Performance” blog series, I’ve been looking at the performance of a 2 TB Crucial P2 NVMe SSD I installed in my Lenovo X13 notebook. While it did it’s job well, I was rather underwhelmed with performance. So after a few weeks, I replaced that drive with a 2 TB Samsung 970 Evo Plus NVMe SSD. As the specified write capabilities of that drive goes far beyond the speed I could read data from any other drive I have for testing, I set up a RAM disk with a huge file on it in the second part of this series. So here’s part 3 with my performance results for the Samsung 970 Evo Plus in combination with my X13 notebook when reading from RAM disk, and performance results for my real world scenarios:

Real World Performance – Part 2 – The RAM Disk

In the first part of this “Real World Performance” series, I’ve been looking at the performance of the 2 TB Crucial P2 NVMe SSD I bought for my new notebook. While it does its job, its major weakness is that continuous write throughput is only 100 MB/s. So I bought a top of the line Samsung 970 Evo Plus drive that, according to the specs, should have a much higher continuous write performance.

To be able to test the SSD in a “real world” scenario, i.e. by writing huge files to it, I needed a way to write data to the drive as fast as possible. Writing 0-bytes is probably quite straight forward, but I wanted to have random data to escape any type of compression anywhere in the software chain. The solution: A file with random data on a RAM disk.

When You Read About 0-Days, It’s Probably Too Late Already

Last week on Thursday, I read about the release of a fix for a new Apache 0-day vulnerability that was already exploited in the wild. At first I was a bit concerned, because I run quite a number of VMs with Apache on it. Fortunately, it turned out pretty quickly that my servers were not affected. However, after checking my web server logs, I noted that if my systems had been vulnerable, I would have been hacked long before I read the first article in my RSS stream. Hackers don’t sleep, the press is slow, and I’m even slower!

Real World Performance – Part 1 – NVMe SSD

When I recently bought my new Lenovo X13 notebook with an AMD Ryzen 7 4750U CPU with 8 cores / 16 threads, I had to make a small compromise: I had to buy a rather low end 2 TB NVMe SSD to replace the small SSD it came with, as more expensive but better SSDs would not have reached me in time. It turned out pretty quickly however, that this SSD had a significant downside: The amount of data that can be written to it at full speed is quite limited and any write operations afterward are very slow.