8.0-RELEASE: disk IO temporarily hangs up (ZFS or ATA related problem)

[Alexander Zagrebin]

> > May be a problem is in ata? WD15EADS is a "green" series of drives.
> 
> The WD green drives have a feature called Time Limited Error 
> Recovery  
> where the disk can spend several minutes trying to read a bad 
> block etc.
> 
> It plays havoc with RAID arrays which is why WD recommend you don't  
> use the green drives in arrays. They have more info about the  
> "feature" in the WD FAQ/knowledgebase

I think this recommendation is related mostly to hardware raid controllers.
Also, if to suppose the such drive errors, then "reallocated sectors count"
in the SMART
wouldn't be zero. But SMART data is ok.

$ sudo smartctl -A /dev/ad6 | grep -e "^ID" -e "Reallocated_Sector_Ct"
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED
WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always
-       0
 
-- 
Alexander Zagrebin