Oct 302014

For the dimensions of 19 inch rack mount equipment, see my other post 19 Inch Rack Cases – General Properties.

Rack under the desk

In this project, I was building a rack to be attached to my desk from below. It is accessible from the backside of the desk and holds a switch as well as a 19″ line of power outlets.

Ingredients (listed by their German product names):

  • Adam Hall 6162 Rackschiene
    needed 2*13 = 26 cm
  • To fasten the 19″ equipment you need (for 3 RUs with 4 screws each) 12x:
    • Adam Hall 5666 6Kant Mutter
Oct 302014

I want to run popcount on a large set of 144-byte-long bytearrays. Doing so in Python can be a pita! First, I was using the naive approach with bin(b).count('1') but it was very slow. I did some research on the internet for faster algorithms and I found some. But running an algorithm on a single byte and on a larger set of bytes (Python 3 type bytes with len() = 144) is a different story. So I decided to do some benchmarks with different algorithms:

Oct 212014

Using Samba (or SMB) shares on Linux is not difficult but you should know some tricks. First of all, you can use smbclient to probe your Samba-Server and try to connect to it. You can then mount an SMB-share locally.
In addition, I wrote a tool to synchronize a local directory with a Samba server (without mounting it) via Python. Scroll down for more details.

Using smbclient

To install smbclient and nmap on Arch Linux, do:

pacman -Sy nmap smbclient

Then you can use nmap, nmblookup and smbclient to communicate with your Samba server:

Oct 202014

Der SyncMaster 971P verfügt über ein hochwertiges PVA-Panel, das mit einem sehr hohen dyn. Kontrastwert (4.000:1), einem sehr hohen Betrachtungswinkel von 178°/178° (h/v) und schnellen 6 Millisekunden (G/G) Reaktionszeit aufwarten kann. Das elegante Design verleiht dem SyncMaster 971P der asymmetrische Dreigelenkfuß mit Pivotfunktion, gepaart mit dem versteckten Kabelführungssystem und dem blau beleuchteten Power-Button. Mit dem im Fuß integrierten USB 2.0 Hub (1x Upstream, 2x Downstream) gestaltet sich das Anschließen weiterer USB-Geräte unkompliziert und bequem.

Samsung 971P Dimensions of the Samsung 971P

German product description (ad) and technical specs: Werbetext und Spezifikationen für den Samsung SyncMaster 971P.

Oct 202014

The Dell PowerEdge T20 is a entry-level server from Dell. Being available since 01.2014 the price for those machines dropped quite rapidly in 06.2014 and now end users buy this machine to use it as a cheap desktop computer or workstation. The version with the Intel Xeon CPU 1225v3 is quite powerful and this is the version I bought. This blog post is my collection of information about this computer.

Main Features

  • Processor: Xeon E3-1225v3
  • Graphics (on CPU): Intel HD Graphics P4600
  • Chipset: Intel C226
  • Network: Intel I217
  • Power Supply: 290W
Oct 182014

Details about how a recent Linux sees the card: Intel Gigabit ET Dual Port Server Adapter on Arch Linux (Kernel v3.16)

NIC Bonding on Arch Linux

Simple bonding setup as described in the Arch Wiki:

sudo pacman -Sy ifenslave
cp /etc/netctl/examples/bonding /etc/netctl/bonding
vim /etc/netctl/bonding
# -------- content: ----------
Description="Bonded interface of PRO/1000 ET Server Adapter"
BindsToInterfaces=(enp4s0f0 enp4s0f1)
# ----------------------------
netctl switch-to bonding
# but somehow an IP on a single NIC was left over. So I did:
netctl stop bonding
systemctl stop dhcpcd@enp4s0f0.service
ip link set dev enp4s0f0 down
netctl switch-to bonding
cat /proc/net/bonding/bond0

A more elaborate setup using LACP (802.3ad) mode:

Oct 172014

Serial Communication from UDOO to builtin Arduino Due


stty -F /dev/ttymxc3 cs8 115200 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts

Specs for the UDOO Quad

Source: http://elinux.org/UDOO#UDOO_Quad

Freescale i.MX6Quad, 4 x ARM® Cortex™-A9 core @ 1GHz with ARMv7A instruction set
GPU Vivante GC 2000 for 3D + Vivante GC 355 for 2D (vector graphics) + Vivante GC 320 for 2D (composition)
Atmel SAM3X8E ARM Cortex-M3 CPU (same as Arduino Due)
76 fully available GPIO with Arduino compatible R3 1.0 pinout
HDMI and LVDS + Touch
2 Micro USB (1 OTG)
2 USB 2.0 type A and 1 USB 2.0 internal pin header (requires adapter cable)
Analog Audio and Mic jacks
CSI Camera Connection
on board Micro SD card reader (boot device)
Power Supply (6-15V) and External Battery connector
Ethernet RJ45 (10/100/1000 MBit)
WiFi Module
SATA connector with power header

Oct 162014

Speeding up the write access of a RAID array

echo 32768 > /sys/block/md0/md/stripe_cache_size

Source: Stackoverflow

Speeding up RAID1 array rebuild


echo 50000 > /proc/sys/dev/raid/speed_limit_min
echo 200000 > /proc/sys/dev/raid/speed_limit_max

the resync speed went from 1M/sec to about 25M/sec:

cat /proc/mdstat

Personalities : [raid1]
md1 : active raid1 sdb3[0] sda3[1]
      410024768 blocks super 1.2 [2/2] [UU]
      [>....................]  resync =  0.7% (3086912/410024768) finish=625.8min speed=10836K/sec

unused devices: <none>

Probably you may also change something here:

for syncmd in /sys/block/md1/md/sync*; do echo $syncmd; cat $syncmd; done

Watching the rebuild process:

Oct 142014

This is simply a Bluetooth compatible keyboard.

Pairing with a PC / Tablet

  1. Switch the keyboard off.
  2. Enable Bluetooth on your PC or tablet and search for bluetooth devices.
  3. Press and hold the [FN] button of the keyboard.
  4. Switch on the keyboard.
  5. Select the keyboard on your PC or tablet and wait for a request to enter a passphrase.
  6. Release the [FN] key.
  7. Enter the passphrase and press [Enter].
  8. Start using the keyboard.

The keyboard can only be paired with one PC or tablet at a time. Pair it again if you want to use it with a different device.