Flash storage && performance engineering

LED matrix characters

I’ve tinkered with electronics since I was young (I used to have quite the collection of electric and electronic parts, mostly junk, porbably), but for some reason I lost interest until Arduino came on the scene (of course working for a hardware company helped too). I bought an Uno and built a couple projects on it, and then Raspberry Pi caught my eye. Here was a whole computer, complete with Linux, in about the same size footprint.

Map block devices to iSCSI targets

This is just a quick hack but it might be useful to someone. With open-iscsi you can use “iscsiadm -m session -P3” to see which sessions provide which block device, but the output is long and not the easiest to grok. For example, I have an initiator with 2 LU’s, each LU mapping to a different target. I want to verify which is which because mpathc is giving me less performance than the other.

Graphviz for lab configuration visualization

Setting up my lab environment for testing can be messy and confusing. I’m not just talking about the cable mess, but also how my 8 initiator systems are going to connect to my 2 target systems so that they’ve each got multiple paths. Different multipath options affect the resulting performance numbers, so it’s important to have the multiple paths. To help me visualize how I was going to have to address my NICs (for a 40Gb/s iSCSI test) for an even distribution between my initiators, I started by drawing it out on paper.

Matching LSI RAID volumes to Linux volumes

If you use LSI RAID controllers and have the tw_cli tool installed in Linux, you can correlate the LSI RAID volumes with Linux volumes by matching their serial numbers. So with tw_cli, assuming you’re interested in the first unit of controller 4: tw_cli /c4/u0 show serial And you’d probably run that for all your volumes. Then on the Linux side, you can use udevadm: udevadm info --query=property --name=sda | grep

iTerm and dir_colors

When using iTerm2, if you duplicate the default profile, the reported terminal type (Preferences->Profiles->Terminal->Report Terminal Type) is set to xterm-256color. Some distributions, like the CentOS 5 server I just logged into, don’t have a condition for the xterm-256color TERM type in the /etc/profile.d/colorls.sh script. As a result, you won’t get color output from ls. Changing my iTerm profile to xterm-color gave me colored ls output on my next login without having to putz around with dircolors.

Hello New World

A new job means setting up new computers and getting comfortable in your environment. As a seasoned ops guy I’ve shied away from getting too comfortable in any given environment, because when you’re dealing with a constantly growing production environment less customization is better. Vim is a good example. It sucks to log into a machine, fire up vim, go for your favorite keymapping (like F3 for NERDTree), and realizing it’s just not available.