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I have a PowerEdge 2850 server that used to work well under CentOS 5 i386. It was used with Asterisk as a telephony server, hooked up to the world via a T1 line.

I've since wiped it and installed CentOS 6 x86_64, and everything works well as long as you boot from the install media. As soon as you reboot from the installed image, things slow down to a crawl. It takes about a second for every letter typed on the local console to appear on screen. SSH access through the network is abysmally slow as well. Hard drive read speeds are around 0.5mbytes/s. Same thing happens on CentOS 6 i386. Updating the system using yum doesn't help.

A T1 line from a Cisco router is plugged into the T1/E1 card.

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The problem is that the default CentOS configuration loads the netjet driver for the Digium card, and that driver is the root of the problem. This driver is not the right driver, it doesn't make any sense to use it with Digium telephony cards. As soon as you rmmod the driver, the system's performance recovers. One can turn the driver off in /etc/modprobe.d/blacklist.conf by adding the following line:

blacklist netjet

To use the card, you'll need to install dahdi-linux with appropriate driver package, and configure it for your card.

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