Strange behaviour when read over NFS

[blckhm]

Hi everone,

I have a strange problem during these days when I tried to service jpg,png,gif files from freenas to nginx(ubuntu) over NFS.

I've never tried before service chunky files like png on NFS. When I bring online our systems to serve static content from freenas, write operations occurs on disks while only reading be in question.

I did not know whats under the hood in arc calculations. Maybe last access times of files should written on disks so these write operations comes from that. Or Maybe NFS nature makes write operations when read occurs.

Our system is;
FreeNAS-11.1-U4
Intel(R) Xeon(R) CPU E5-2630L v3 @ 1.80GHz
53209MB
LSI 3008
4x 12TB WD Gold

Used Space: 8.2TB (avg file size of these static content is 200kb)

 

[SweetAndLow]

You only have nfs usage? Nothing else like jails or other services? Something else is writing to the system.

 

[blckhm]

You only have nfs usage? Nothing else like jails or other services? Something else is writing to the system.

Yes, correct. We've only nfs usage on this drives for serving static content as I said before. I also made a mini test about that issue.

When I unmount the nfs directory on webserver, all read and write operations disappears from charts. only few write operations exist (5-10 write ops/sec) because of FTP service is still writing new files to tank.

After that, I remount the NFS directory to web server and start serving the content from NFS, write operations are started to rise up again.

 

[SweetAndLow]

Yes, correct. We've only nfs usage on this drives for serving static content as I said before. I also made a mini test about that issue.

When I unmount the nfs directory on webserver, all read and write operations disappears from charts. only few write operations exist (5-10 write ops/sec) because of FTP service is still writing new files to tank.

After that, I remount the NFS directory to web server and start serving the content from NFS, write operations are started to rise up again.

Well something on that host is writing to the nfs export. Freenas is updating access time but there are more writes than reads so something else is writing.

 

[blckhm]

Well something on that host is writing to the nfs export. Freenas is updating access time but there are more writes than reads so something else is writing.

Could you explain more detail about updating access time, please? I think this meta is necessary for ARC determination which files goes under cache, is not it?

 

[SweetAndLow]

No the access time when the file was last accessed. That has nothing to do with how arc gets filled. Arc is based on blocks. Why would your read cache have anything to do with your disks seeing writes?

 

[blckhm]

Well something on that host is writing to the nfs export. Freenas is updating access time but there are more writes than reads so something else is writing.

I've just checked again all NFS shares and found 1 virtual machine how makes a few write ops. and shut it down.

I attached new charts at below;


And I still get same amount of write operations for every read..