Re: [CentOS] High load averages copying USB

On Fri, Apr 20, 2012 at 12:42 AM, Lists lists@benjamindsmith.com wrote:

Problem as follows:

1. Plug in an external USB drive.

2. Mount it anywhere. Doesn't matter how.

3. Copy a few GB of data to the drive from a non-USB disk.

4. Watch the load average "climb" to 5.x, sometimes 10.x or more. Why?

This on an otherwise unloaded system. Doesn't matter how many cores, how much RAM, 32/64 bit, etc.

Why should copying some files to a USB drive cause load averages to climb so high? (and network monitors to freak out?)

The CPU has to do the work of the transfer over usb - which is why it is cheap. Real disk controllers use DMA without a lot of CPU involvement.