FreeBSD-6.1 bootup hangs after power failure

Peter Schuller peter.schuller at
Mon Jul 16 16:23:52 UTC 2007

> One thing I find FreeBSD very fussy and sensitive in comparison to Linux
> OSes is that whenever there is an power outage, something wrong is bound
> to happen. Maybe, it was made to happen this way but living in here over
> the other side of the world, we do have to face power outages despite
> our best efforts.

The problem with power outtages is that in the presence of write caching *all* 
bets are off. In practice I have found this a bigger problem with UFS2 than 
with e.g. reiserfs on Linux; possibly because the characteristics of disk i/o 
in those cases make it less probably to actually trigger a problem in 
practice (but this is just my speculation, but fits my experiences).

But regardless, all bets *are* off in the event of a power outtage. Unless you 
have battery backed caching controllers, you will need to disable write 
caching (hw.ata.wc=0) in order to be safe - at the cost of performance.

Alternatively for 7.0+ or CURRENT you can use ZFS which understands these 
things and will actually send cache flush commands to the drives on 
transaction commits, thus allowing safe operation in the event of a power 
failure, while not taking the performance hit associated with disabling write 

/ Peter Schuller

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