Marc's Public Blog - Linux Hacking

In my case, I picked up an 8 port ftdi usb to serial converter for only $15 on Ebay (woot!) but even its ports may not come up in sequence at boot time if other modules are loaded at the same time (a race condition can cause the pl2303 port to be in between one of the 8 ports from the ftdi hub).

Turns out there is a solution to this problem with udev, iff your usb to serial adapters have serial numbers (my ftdi ones did, but my pl2303 ones did not), or if you only have one serial adapter of each brand (like ftdi, pl2303, keyspan).

In my case, I have (don't laugh), 11 serial devices on my server:

This is what you do with udev:

gargamel:~# cat /etc/udev/rules.d/50-local-usb-serial.rules 
# /etc/udev/rules.d/50-local-usb-serial.rules

# http://www.reactivated.net/writing_udev_rules.html#udevinfo
# was udevinfo -a -p /class/tty/ttyUSB0
# now udevadm info --attribute-walk -p /class/tty/ttyUSB0

SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A7006gvN", SYMLINK+="usb-serial-ftdi-8_1"
SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A7006gvO", SYMLINK+="usb-serial-ftdi-8_2"
SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A7006gvP", SYMLINK+="usb-serial-ftdi-8_3"
SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A7006gvR", SYMLINK+="usb-serial-ftdi-8_4"
SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A7006gvQ", SYMLINK+="usb-serial-ftdi-8_5"
SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A7006gvS", SYMLINK+="usb-serial-ftdi-8_6"
SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A7006gvT", SYMLINK+="usb-serial-ftdi-8_7"
SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A7006gvU", SYMLINK+="usb-serial-ftdi-8_8"

SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A800dMFk", SYMLINK+="rfxcom"

SUBSYSTEMS=="usb", ATTRS{product}=="USB-Serial Controller", ATTRS{manufacturer}=="Prolific Technology Inc.", SYMLINK+="usb-serial-pl2303"

After making a change udevadm trigger will update symlinks.

My original gargamel server

This server worked a good 6 years or so, and I eventually replaced it in 2006 with a dual P4 Xeon server board I got from my new then work. Drives also got bigger, so I removed SCSI and the 3 external disk arrays, switched to SATA with port multipliers, and settled with 12 internal drives (2 boot drives, 5x250GB and 5x500GB) for a total usable space of 3TB with a "much lower" power usage. Typical power was now in the 280-300W range for the entire server closet.
Note that my base usage in the closet with computer off is still 70W (UPS is 23W by itself, cable modem and 24 port switch is another 30W, and the other random stuff brings it to 70W).

Gargamel V2 with Sata and PMP

Eventually, another 5 years later, I was tired of debugging a couple of issues with the server that was sometimes low on memory that was hard/expensive to find vs bigger DDR3 dims. I also wanted to reduce the power consumption of that power hungry P4 Xeon Server board. One thing I did that helped a while ago was to write some software to make sure all the drives suspended (spun off), which explains the big spikes in power (drives spinning or spun down). See my Spinning down WD20EADS Drives and fixing load cycle page.
Thanks to help from coworkers who followed PC trends, I went for an Intel Sandy Bridge MB (it was hard to find one with a serial port for serial console booting, and onboard IDE, and 2 PCI slots, but eventually I think I got the last one available :) ). I paid a few dollars extra for an Intel i3 2100T dual core CPU, which is only 2.53Ghz, but that's more than plenty and it only uses 35W, which is awesome.

As a result, I came down to about 270W average for the computer closet (200W for the computer) to about 210W average (140W for the computer). It will now full idle at 180W (110W for the computer). Sure, one might say 110W is still a lot, but for a server with 10 drives, I/O cards, around 16 USB devices connected, dual ethernet, and dual sound (5 + 7 channels), that's not so bad. In the end, the power graph looks better, so that's good enough for me :)

The hole is where I changed the server

The here Christened Gargamel V3!

all wired up