What did the sar -d look like for the 2 minutes before and 2 minutes
afterward?
If it is slow or not may depend on if the directory/file fell out of cache
and had to be reread from the disk.
I have also seen really large dirs take a really long time to find, but
typically that takes thousands of fines in a dir. if you do ls -ld
<dirname> you will see how big the dir is if the dir is really big under
some condition that can be slow, but usually not 45 seconds.
On Sat, Oct 2, 2021 at 12:00 PM Terry Barnaby <terry1(a)beam.ltd.uk> wrote:
I am getting more sure this is an NFS/networking issue rather than
an
issue with disks in the server.
I created a small test program that given a directory finds a random file
in a random directory three levels below, opens it and reads up to a block
(512 Bytes) of data from it and times how long it took to find the file
(opendir/readir) and read the block from the file printing the results if
the time is greater than previous ones (so seeing the peek times). This is
repeated every 10 seconds. First param is the average time to find the file
(there may not be a file 3 levels down so it repeats those searches untill
it finds one that the user can access), the second is the time it took to
find the file (3 x opendir/readdir) to a file that existed. the last time
is how long it took to open, read and close the file.
I set one of these processes running on the server starting at the /home
dir and did the same on one of my clients that has /home NFS V4 mounted
with defaults + async.
The server after 12 hours had peak timings of (file paths hidden):
2021-10-02T09:26:38 0.008858 0.043513 0.031735 /home/...
2021-10-02T09:26:58 0.005384 0.050870 0.039186 /home/...
2021-10-02T09:38:09 0.006684 0.081707 0.014616 /home/...
2021-10-02T10:18:42 0.037394 0.144025 0.012603 /home/...
The client had timings of:
2021-10-02T08:48:45 0.056195 0.110149 0.019353 /home/...
2021-10-02T09:06:31 0.098647 0.098647 0.015171 /home/...
2021-10-02T09:28:38 1.060605 0.001996 0.000422 /home/...
2021-10-02T09:31:28 4.896196 2.037488 0.000836 /home/...
2021-10-02T11:48:44 4.423502 7.087917 1.111684 /home/...
2021-10-02T11:51:02 27.711746 45.646627 0.021321 /home/...
So at one point the NFS mounted client took 45 seconds to find a file
(opendir/readdir 3 times) and once before 7.08 seconds with 1.1 seconds to
read a block. The actual file it accessed is
46819 Bytes long and can be normally quickly accessed/copied etc.
"sar -d" reported no issues.
"mountstats /home" reported no issues
"/var/log/messages" in both systems reported no issues.
Generally the desktop system has been responsive all day (no other users
and nothing obvious going on on both server and client) and I have not
noticed a "lockup" on the GUI I have been using (intermittently). No
noticeable network errors, no noticeable hard disk read issues, but
occasional very long NFS opendir/readdir which would match up with when i
see the desktop lock up for around 30secs ore more.
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