System comes to a halt on heavy disk I/O

Charles Curley charlescurley at charlescurley.com
Mon Feb 1 13:45:28 MST 2010


On Mon, 01 Feb 2010 13:18:16 -0700
Shane Hathaway <shane at hathawaymix.org> wrote:

> 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 that. I've seen "hdparm -t" return in the 100 KB/s range.

> 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.

Yeah, I've been suspecting hardware issues. I got the system in
December 2007, and added this hard drive November 2009. So I suspect
it's the drive.

I don't see any evidence of failure in the SMART data, but that's not
conclusive.

Mr. Burgener's suggestion to use vmstat narrowed the suspicion to
somewhere below the hard drive driver level, which certainly includes
the hard drive. That's why I think testing with sda might be useful.
(sdb being the current drive.)

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