Blogs

Here you can find a list of all my blogs published here.

  • How to add a new disk to RAID5
    I have a RAID5 consisting of three 10TB HDDs. This RAID5 has a total capacity of 20 TB. I bought a new 10 TB HDD that I want to use to extend the RAID5: 4 HDDs with a total capacity of 30 TB. The file system on md0 is ext4. Currently, the RAID5 disks are sdc1, sdf1 and sde1. The additional disk is sdd1. cat /proc/mdstat The RAID5 is formatted with ext4 and available as md0. mount Steps Prepare new disk Add disk to RAID Grow RAID Extend ext4 files system. Prepare new disk First start with the preparation of the new disk. The disk is /dev/sdd and needs to have a partition. I use parted for this. First, create…
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  • Monitor disk speed in Linux
    Running a server allows you to do a lot of stuff from remote. Copying files is one of those tasks you can do from anywhere on the world while being logged on via SSH. For this task it is good to know the speed of read/write to get an idea if it’s working s expected. When sitting in front of your computer, you can see if a HDD is working, in Windows you see a MB/s indication, and in Linux? Not all copy commands show you the transfer rate by standard. Some disk intensive tasks won’t at all (RAID sync). To monitor disk activities in Linux, several tools are available. One is iostat. Installation To install iostat in Debian, you…
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  • Increase RAID sync rate
    Scenario The HDDs are in an external USB case. RAID5 with 3 HDD (10TB) Software RAID5 with mdadm and Debian Linux Adding a new disk When you add a new HDD to an existing RAID, a sync is started. In my case I added a 10TB disk to a RAID5. The sync started and as estimated time I got something in the range of days. The estimated time is listed in finish=5384 min. This number goes up and down a little bit, but overall result is that the sync will need days. After checking the status again after a while, it still showed days: finish=3437min. The main problem here Is the rate at which mdadm can sync the data. The…
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  • Assign a static IP to DHCP client
    After setting up a DHCP server on a Raspberry Pi running Linux I get working leases for my clients. However, these are not static. It can happen that my smartphone gets a new IP address the next it connects: 192.168.0.161 instead of 192.168.0.160. For some clients I want to make sure they always use the same IP. This can achieved with ISC DHCP Server by registering a static lease for a specific MAC. Example I’ll use my soundbar for the rest of this blog as an example. The MAC of the network card is bc:30:d9:2a:c9:50. I want to always assign the IP 192.168.0.152 to the soundbar. Find out client data To find out the client data like MAC and current…
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  • DHCP Server on Linux with Raspberry Pi
    My internet provider is Unitymedia. Their default router comes with a DHCP server. Honestly, it’s one of the worst products I ever had to work with. My private network is 192.168.0.x. The DHCP server of the Unitymedia box is distributing from time to time leases for 192.168.192.x. Changing my private network to 192.168.192.x one is not working, as then the DHCP server picks another address range. Advise from Unitymedia help desk was to reboot the box, which, of course, won’t solve the problem. Because of this error, some of my devices are in a different network: Chromecast won’t work, broken internet connection on smartphones, etc. I do have a Raspberry Pi (RP) in 24/7 use. My idea is to run…
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  • Apt-get unable to connect to IPv6 address
    Recently I had the problem that running apt-get update stalled while trying to connect to an IPv6 address. For instance, on a Raspberry Pi, the update process stalls while trying to connect to archive.raspberrypi.org. All other connections worked fine. Looking at the console output, a difference was that apt was trying to connect to an IPv6 address. The problem was caused by: 100% [Connecting to archive.raspberrypi.org (2a00:1098:0:80:1000:13:0:8)] A quick internet search showed that you can force apt to not use IPv6 and only IPv4. As the download worked for IPv4, this seems like a reasonable workaround. Solution You can pass a parameter to disable IPv4 to apt-get, or write it to apt config file to make it persistent. Configuration file…
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  • Partitioning and formatting a large disk
    I got a new 10 TB disk. Before I’ll add this one to a RAID, I want to play around with it, aka: test the drive. Therefore, I’ll need to format the drive to mount it. And before that, I need to create a partition. FDISK In the good old days, you used fdisk to partition a HDD. Since a few years, fdisk was replaced by parted as fdisk got some issues with large. Nevertheless, it still works. Make sure to create a GPT partition table (g), and not the old new partition (n) alternative. Creating a new partition using “n” gives you a 2 TB partition. Creating a new disklabel of type GPT using “g” gives you 10TB. The…
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  • Ideen für 2019
    2019 ist schon ein paar Tage alt, Zeit die Ideen zu sammeln und einen Plan für 2019 und 2020 zu Erstellen. Seit meiner Rückkehr nach Deutschland habe ich die Idee den SAP Community Erfolg aus Brasilien in Karlsruhe und Umgebung zu wiederholen. Rückblick In Brasilien habe ich maßgeblich dazu beigetragen das die SAP Inside Tracks von einem Event von wenigen Nerds zu einem Erfolg wurde. Der Prozess lief leider nicht ganz reibungslos, da man hierbei festgezurrte Denkmuster durchbrechen muss, und nicht jeder mag Veränderungen. Davon profitieren ja, aber aktiv mitgestalten? Was zählt ist aber auch das Resultat. Von einem SIT in Sao Paulo mit etwas 20 Leuten hin zu einer ganzen Menge an SITs in verschiedenen Städten mit um die…
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  • State of the art documentation from SAP
    SAP is investing heavily in marketing the Fiori for iOS and the SDK. In case you are slightly interested in Fiori and UX in general in SAP, for sure you heard a lot about the SDK. 2 ½ years after the announcement the Fiori Design guidelines include an iOS section, there are SAP Developers tutorials, a special iPad app for learning its usage is available, even Apple has set up a Fiori page. Current version of the SDK is 3.0, and now there is even an Android version available (with much less marketing activities). If you want to write an app with the SDK, make sure you have an iPad. The online SDK documentation is available too, but offers less…
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  • Remove last n characters of file in MacOs
    With MacOS and finder you can easily substitute characters of files using the rename functionality. Just select 2 or more files, right click, and inform the character you want to substitute, like _ with space. To remove the last N characters from a file that looks like Text-2018221112.mp4 to Text is more complicated. The rename dialog does not understand regex. What you can use is the shell and rename Install rename brew install rename Go to the directory with the files and run rename -n 's/.{11}.mp4/\.mp4/' * Rename uses the well known sed syntax s/char/replace/. -n runs the replace in simulation mode. It will print the result, without renaming the files yet. Perfect for testing. {11} number of characters to…
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