kmem panic in FreeNAS 8 stable

[ronch]

Hi,

I built a new system trying to be low power so I used an Atom processor (so it's 32-bit) with 4 2T drives and 4G of RAM (system on a USB stick). I found the same error being reported (http://forums.freenas.org/showthread.php?256-vm.kmem-Size-Error-and-Prefetch&highlight=kmem+panic) in a few posts (including some every old ones) with the solution to add:
vm.kmem_size="512M"
vm.kmem_size_max="512M"

to /boot/loader.conf.

While the kernel will boot and initially run, it also panics just later in time compared to not setting the value. It is always reproducible. I just have to start copying 10-20 gig of data to the ZFS CIFS share. I found another post (http://forums.overclockers.com.au/showthread.php?t=964272) which said make it even bigger (3g instead of 512M. The system won't boot up at all with this setting.

Is somebody working on this issue? Since I want to use the Atom for the power savings moving to a full high end 64-bit system isn't a solution. I might have to move to OpenFiler or something like that if this can't be resolved.

 

[survive]

Hi ronch,

Are you sure your Atom isn't 64 bit?

Intel has released both 32 & 64 bit Atoms, if you know what chip your system actually uses have a look at the chart here:

http://en.wikipedia.org/wiki/Intel_Atom

That said, ZFS with 32bit processors has always been pretty temperamental and it does take some tweaking to get it working right.

If your Atom does support 64bit then just run the AMD64 build and forget you ever had the problem, if not...personally I'd box the board back up and return it and get an Atom that does.

-Will

 

[ProtoSD]

I agree with Will, if your Atom board is new, it's most likely 64bit. I went thru the routine of recompiling my kernel to allow for tweaking the settings for RAM for the same problem you're having only because I didn't realize the AMD64 version also worked for Intel processors and it's saved me the hassle of recompiling everytime an update happens.

Thanks again to the person that pointed that out to me! ;-)

Oh, it's also worth mentioning that my 64bit Atom system only uses 46 watts idling and peaks about 60 watts during heavy activity, like a scrub. The 160w Pico power supply handles the 6 drives and motherboard with room to spare.

 

[ronch]

Thanks guys, you were correct that the Atom I have can be run in 64-bit mode. My setup is very similar to protosd's. Since I've gone to the 64-bit version things have been running great. It does make me a bit nervous that there is so much difference between the 32-bit and 64-bit versions that one can have such a serious panic in it however. Anyway, thanks again. Things are working well right now.

 

[survive]

Hi ronch,

I wouldn't worry to much about the instability you saw when you were running the 32 bit version. Keep in mind where ZFS came from compared to the platform you were trying to run it on...

ZFS came from Sun Microsystems and was used on their "big iron" systems and migrated down to smaller systems over time. I like this quote from Wikipedia article on ZFS that underscores just how big Sun was thinking:

"ZFS is a 128-bit file system, so it can address 1.84 × 1019 times more data than 64-bit systems such as NTFS. The limitations of ZFS are designed to be so large that they would never be encountered. This was assured by surpassing physical rather than theoretical limitations—there simply is not enough useable matter on the planet Earth to support a maximized ZFS filesystem."

http://en.wikipedia.org/wiki/Zfs under "capacity"

Remember that you were trying to run that on an i386 system whose core dates from back when a megabyte was a serious amount of ram! The i386 instruction set contains 30 plus years of hacks and workarounds to maintain backward compatibility with all sorts of hardware and to put it bluntly it shows. Take a look at this article (one of my favorites) to get an idea of the sorts of things the move to AMD64 has improved:

http://www.dansdata.com/askdan00015.htm

-Will