ARC Hit Ratio <25%

[peter-swe]

Hi guys
Since I've upgraded our server (i'm not sure at what upgrade this happened though, currently at 9.10.2-U1 ) the ARC Hit Ratio is Really low. 24% right now.
When I first got this server started we had a stable 98% and not much has changed except for more files on the server.

Platform Intel(R) Core(TM) i3-2120 CPU @ 3.30GHz
Memory 32428MB

5 disks at 4 TB each (20 TB)
Volume at Raidz2

What could make this huge drop? I'm guessing it can and will effect the performance though right now it seems to be OK.

 

[dlavigne]

This bug is currently under investigation: https://bugs.freenas.org/issues/20654.

 

[peter-swe]

This bug is currently under investigation: https://bugs.freenas.org/issues/20654.

Thanks for the reply!

 

[Kevin Horton]

There was a huge change in ARC hit ratio with the update to 9.10.2. Earlier versions had a bug in a maintenance task that caused some files to be read very frequently, which caused the calculated arc hit ratio to be abnormally too high, as these files would always be found in the ARC. 9.10.2 fixed this bug, so the ARC hit ratio better reflected reality. Lots more info in this thread, especially this post. Bottom line - the actual ARC hit ratio is likely unchanged.

 

[m0nkey_]

the ARC Hit Ratio is Really low. 24% right now.

@DrKK and I conferred with Allan Jude regarding this. What you're seeing is now normal.

https://forums.freenas.org/index.ph...rc-usage-in-freenas-9-10-2.48831/#post-336818

Mine has pretty much averaged out around the 50% mark with an uptime of 32 days and normal use.

 

[peter-swe]

Cool. We had a lot less RAM earlier and got bad performance and bad ARC Hit Ratio. Added RAM and got 98% and huge performance increase.
And I really haven't seen any performance loss which made me confused.

Anyhow, thanks for the answers. All is well!