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njcwotx Guru
Joined: 25 Feb 2005 Posts: 587 Location: Texas
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Posted: Thu Nov 30, 2017 9:29 pm Post subject: sysstat 'sar -d' output shows writes during a find [SOLVED] |
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This is a sysstat usage question, but I generally find good answers here...
see systat results line.....
Code: | 12:00:01 AM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util
12:10:01 AM dev8-64 260.59 63045.3 61786.47 479.03 36.05 138.38 3.84 100 |
the device is obviously slow, but I'm curious about the 61,000 "wr_sec/s". I know when the process stops, the wr_sec goes to nearly nil.
this is a sample of the command running during the data shown.
Code: | cd "to a folder on dev8-64..."
find . -type f -name '*.hl7' | xargs cp -t /some/other/device/not/dev8-64 |
Everything but he wr_sec/s seems expected, but I cant fathom why the wr_sec are just as high as the rd_sec/s. Is there some way find works that it has to write back to the filesystem with some update?
[Moderator edit: added [code] tags to preserve output layout. -Hu] _________________ Drinking from the fountain of knowldege.
Sometimes sipping.
Sometimes gulping.
Always thirsting.
Last edited by njcwotx on Fri Dec 01, 2017 8:36 pm; edited 1 time in total |
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Ant P. Watchman
Joined: 18 Apr 2009 Posts: 6920
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Posted: Fri Dec 01, 2017 12:45 am Post subject: |
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The most likely explanation I can think of is that you have atime updates enabled. Still seems a bit high, even for that.
One worse theory is that the disk's failing and busy trying to relocate damaged sectors, but I don't think that'd show up in userspace stats... |
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njcwotx Guru
Joined: 25 Feb 2005 Posts: 587 Location: Texas
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Posted: Fri Dec 01, 2017 8:35 pm Post subject: |
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access times is the issue.
mount /vol -o remount,noatime
and the writes disappeared! Latency went from 138ms to 1ms, thats a huge difference.
app team was copying millions of tiny files, this increased their performance significantly. Nice to know I can always count on people here to answer up with good info! I recall many years ago a simliar issue with some CAD software reading thousands of part files and this helped as well, I had forgotten until I changed the mount option. _________________ Drinking from the fountain of knowldege.
Sometimes sipping.
Sometimes gulping.
Always thirsting. |
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