[CentOS] High load averages copying USB
Les Mikesell
lesmikesell at gmail.com
Fri Apr 20 14:54:51 UTC 2012
On Fri, Apr 20, 2012 at 12:42 AM, Lists <lists at 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.
--
Les Mikesell
lesmikesell at gmail.com
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