Quoting Christer Solskogen <[email protected]> (from Tue,
16 Nov 2010 13:15:32 +0100):
On Tue, Nov 16, 2010 at 12:47 PM, Ivan Voras <[email protected]> wrote:
You can easily test it - use the stick as a simple disk device with UFS and
see how much CPU does it take simply to talk to the device.
See, that is why I think it is a ZFS issue. Because I did that.
I created a UFS filesystem on the same usb stick. Mounted it and did a
"dd if=/dev/zero of=/mnt/file".
The systemload goes +0.6 instead if +10.3.
See:
CPU: 0.0% user, 0.0% nice, 0.6% system, 0.0% interrupt, 99.3% idle
Mem: 832M Active, 960M Inact, 7017M Wired, 2600K Cache, 1237M Buf, 3063M Free
Swap: 8192M Total, 8192M Free
PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
38261 root 1 46 0 5776K 1112K wdrain 7 0:07 4.98% dd
But when using it as cache device for zfs:
CPU: 0.0% user, 0.0% nice, 11.9% system, 0.0% interrupt, 88.1% idle
Mem: 832M Active, 193M Inact, 5782M Wired, 2592K Cache, 1237M Buf, 5066M Free
Swap: 8192M Total, 8192M Free
The funny thing is that when I add the device (and some cache is added
to it) the load is normal. But the load goes up when nothing is
written to it (or beeing read from it)
How do you measure that nothing is read or written to it?
Please check with
gstat -f '^<DEVICE>$'
if there are really no reads/writes to the device (please replace
<DEVICE> with the name of your USB device, e.g. da0).
If you see writes, I would say
- this is the reason for the load
- your cache is on the way to be filled with
useful data
If gstat shows zero activity, I suggest to run 'top -S' and look at
the process(es) which consume about 10% CPU (do not take care about
the idle process). Based upon this we can maybe suggest further things
to investigate.
Bye,
Alexander.
--
Is a tattoo real, like a curb or a battleship? Or are we suffering in
Safeway?
http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID = 72077137
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