[linux-lvm] High loads when writting to LVM
pdw at ex-parrot.com
Wed Oct 27 15:27:40 UTC 2004
On Wed, Oct 27, 2004 at 11:14:05AM -0400, Judd Tracy wrote:
> I have a system that I am testing out lvm on to get a feeling about
> stability and performance. Stability right now seems good, but I am a
> little worried about the performance currently I am writing out a large
> file ~1TB using dd if=/dev/zero of=test bs=1M and am noticing the load
> seams extreamly high "5.21, 5.26, 5.17". Most of the work is being done
> in dd but I also notice that kswapd0 is also working fairly heavily. Is
> this to be expected with LVM or do i have things setup wrong. Write
> performance seems to be around 100MB/s on an XFS filesystem.
This may be a result of how load average is calculated. What is the CPU
usage when doing these (see top)? On a machine with a large number of
processes accessing the disk, it is quite easy for a single, I/O
intensive application (such as your dd) to drive the load up.
The load average is telling you that you have 5 processes blocked
waiting for I/O. Without the dd, the time taken to service each is
reduced, and the average number blocked at any given time is therefore
On our combined shell/web/email server, an I/O intensive process will
result in a load of well over 10, yet responsiveness of the system
is not actually that bad, and cpu usage remains low.
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