sysctl in GUI has no effect?

[cyberjock]

Autotune only adds entries to sysctls and tunables, so unless you have 2 entries for the same setting then no.

 

[datnus]

The sync random write is only 20 Mbps. FreeNAS says so
So two seconds, only 40 Mb or 5 MB.
Then why not?

As random write is a killer. It makes my hdd busy% reach 100%
The throughput is small.

Um, you can't convert random IO to sequential IO the way you think you can. All IOs are somewhat(kind of) converted to sequential as long as they aren't sync writes.

I will tell you that setting your timeout to 120 seconds is going to be a very very very big mistake. You are going to possibly have issues where the data written will take 10+ seconds to write every 120 seconds. In essence, your system will be really fast for 120 seconds, then be completely unresponsive while it writes all the data in RAM to the pool. For your own sake you should be hoping to have LOTS sync writes so that the system doesn't go catatonic. Of course, that defeats the purpose of what you are trying to do. And if you only have 16GB of RAM you are in even deeper doo-doo because you'll potentially empty out the ARC trying to store all this writable data which will tank your read performance. And don't get me started on what happens if the system crashes. ;)

As for the synctime_ms, it doesn't work quite the same way you think it does either. I'd normally hope one of our mods that knows tweaking better than most would step in, but he hasn't been around in almost a month.

Remember all that stuff I said about tuning not being easy and there's a reason why "evil" is often applied to tuning. I think you're about to find out just how evil tuning can be. I'm assuming you are trying to fix your latency issues from the thread http://forums.freenas.org/threads/latency-spike-for-iscsi.14612/

 

[William Grzybowski]

If it cannot be set using sysctl and is writable then it is a Tunable and need reboot, not a sysctl.