ZFS on AMD64 - any recent crashes?

Travis Mikalson bofh at terranova.net
Sun Jan 6 17:02:00 PST 2008


Ivan Voras wrote:
> Peter Schuller wrote:
>>> In light of the recent discussion about ZFS stability, does anyone still
>>> have kmem_map_too_small panics on AMD64 after tuning it (as presented in
>>> http://wiki.freebsd.org/ZFSTuningGuide)?
>>
>> Not sure if you wanted negatives, but I have not seen such crashes on 
>> any of 
> 
> All reports are welcome :)
> 
>> the three amd64 systems I'm running ZFS on (3 gb, 4 gb and 4 gb of 
>> RAM). The only tuning done is to increase the kmem size and arc_max 
>> and disabling prefetch. The increase in kmem was not to avoid crashes, 
>> but was to accomodate the larger arc_max chosen.
> 
> This is somewhat a special case - you also did tuning besides kmem size. 
> I'm especially interested in this, hoping to gather the "combination 
> that works" from the reports.

I can tell you what works for us. Slightly verbose and repeating things 
most of us already know, for the archives.

Do not put your swap on ZFS.

On an amd64 system with 2GB of RAM, we put the following in 
/boot/loader.conf:
vfs.zfs.arc_max="600M"
vm.kmem_size_max="1G"
vm.kmem_size="1G"

We seem to pretty easily panic our RELENG_7 ZFS systems if we do not set 
arc_max to roughly 65% or less of kmem_size_max. I do 60% to be more 
conservative. YMMV, but you get the idea.

To panic our systems quickly when the tuning settings are bad (in other 
words, to trigger a kmem_map_too_small panic) we can use iozone. It 
usually only takes a minute or two.

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