Archive for July, 2011

How Redhat 5 and Centos 5 detect hardware at boot

With the introduction of RHEL6 our beloved kudzu was removed from Redhat Enteprise Linux (it’s been gone from Fedora for quite some time). If you’re not familiar with kudzu, RHEL5 and below use it to detect new hardware when a system is bootstraped. All of the functionality that was part of kudzu is now handled […]

Kudzu removed from RHEL6

With the introduction of RHEL6 the kudzu hardware hardware manager was removed. All of the functionality that was once a par of kudzu has been integrated into the kernel and udev, as evidenced by this e-mail correspondence with one of Redhat’s support engineers: “Kudzu is removed from rhel6. The kernel should be taking care of […]

Measuring hard drive seek times

I’ve been fascinated with I/O and file system performance for years, and chose prefetch.net as my domain name after reading about pre-fetching algorithms in the book UNIX file systems (a great book that I need to read again). Since most applications access data that is not laid out sequentially on a hard drive platter, seek […]

Speeding up SSH (SCP) data transfers

I’ll be the first to admit that I’m an SCP addict. It doesn’t matter what kind of data I’m working with, if it can be turned into an object that I move around with scp I’m in! One thing I’ve always noticed with scp is the dismal out of the box performance. I read quite […]

Gathering statistics from your postfix mail logs

I have been supporting postfix mail relays for several years. When you are tasked with ensuring that your SMTP relays work without issue, you need to stay on top of the logs and the current operational state of each server to prevent major problems from occurring. Problems can take the form of blacklisted relays, mail […]

Using netstat and dropwatch to observe packet loss on Linux servers

Anyone that is running a modern Operating System is most likely utilizing TCP/IP to send and receive data. Modern TCP/IP stacks are somewhat complex and have a slew of tunables to control their behavior. The choice of when and when not to tune is not always super clear cut, since documentation and the advice of […]