ZFS hang issue and prefetch_disable

[Miroslav Lachman]

Matt Simerson wrote:
> Symptoms
> 
> Deadlocks under heavy IO load on the ZFS file system with  
> prefetch_disable=0.  Setting vfs.zfs.prefetch_disable=1 results in a  
> stable system.

[...]

> With vfs.zfs.prefetch_disable=1, a hang will occur within a few hours  
> (no more than a day). If I keep the i/o load (measured via iostat)  down 
> to a low level (< 200 iops) then I still get hangs but less  frequently 
> (1-6 days).  The only way I have found to prevent the hangs  is by 
> setting vfs.zfs.prefetch_disable=1.

"With vfs.zfs.prefetch_disable=1, a hang will occur within...", did you 
realy mean prefetch_disable=1 in this sentence? Your whole e-mail seems 
that prefetch_disable=1 is good workaround, so I expect you have 
prefetch_disable=0 previously which causes hangs...

Miroslav Lachman