System comes to a halt on heavy disk I/O

[Shane Hathaway]

Charles Curley wrote:
> When I run fairly disk intensive tasks, like copying tens of gigabytes
> to this machine, it slows to a crawl. Disk I/O slows down by two
> orders of magnitude.

Are you saying you expect to be able to write 90 MB/s under ideal 
conditions, but that when you try to achieve that speed, you only write 
1 MB/s?  If so, that's very similar to symptoms I saw when working with 
some bad hardware a few years ago.  The drives would inexplicably slow 
to a crawl during large transfers, yet the same drives worked perfectly 
when attached to different computers.  I never did find the cause, since 
we got rid of those servers, but I suspected that either noisy power or 
vibration was causing the hard drives to frequently position the head 
inaccurately.

Shane