System comes to a halt on heavy disk I/O
kenneth at mail1.ttak.org
Mon Feb 1 09:51:55 MST 2010
On 2/1/2010 9:03 AM, 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.
Linux tends to use disk cache as much as possible, so until you start
performing disk operations that fill all of the available RAM for the
disk cache, things will appear snappier.
While you are performing your disk operations, try watching 'vmstat 2'
under the 'wa' (IO wait) to see what percentage of the CPU time is being
spent waiting for IO. This number should remain as close to zero as
possible. If the IO queue is so backed up that things aren't being
handled prompty, then you will quickly notice IO based apps will begin
to crawl. Adding more RAM usually helps with IO issues, as more of the
disk can be cached to RAM.
Also check 'smartctl -a /dev/sda' and check to see if the error rate is
increasing rapidly. If the disk is spending it's time recovering from
failures, this would decrease the throughput, and also indicates that
the drive is probably going bad.
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