On Wed, Apr 24, 2013 at 01:27:19PM -0400, Jeff Siddall wrote:
> On 04/23/2013 07:20 PM, Konstantin Olchanski wrote:
> >>disk utility show ... SMART [is] fine.
> >>>
> >SMART "health report" is useless. I had dead disks report "SMART OK" and perfectly functional disks report "SMART Failure, replace your disk now".
> 
> Agreed.  SMART doesn't diagnose everything.
> 

Raw data reported by SMART seems solid enough - hours of use, temperatures, bad sector counts, etc.

But the "SMART overall-health self-assessment test result" is useless and
for the purpose of predicting disk failure, all data reported by SMART is useless.

Maybe one exception: when the number of bad sectors starts incrementing rapidly,
the disk often fails soon thereafter.

But more typically I see this scenario:
in the morning - reading the email reports:
smartctl reports increase of bad sectors
disk is dropped from the raid array
smartctl reports that the disk does not support smart (it's way of telling us that the disk died)
cat mdstat shows [U_] we are now running on the spare disk

In other words:
- all disks will fail eventually
- there is no reliable predictor for "your disk will fail in 7 days, rush to newegg now!", 
- to prevent complete data loss, implement rsync to some other disk
- to ensure uninterrupted operation, raid all disk.

This is all in my experience. Your experience may be different and if you now a source
for "this disk will never fail" disks, please let me know.

-- 
Konstantin Olchanski
Data Acquisition Systems: The Bytes Must Flow!
Email: olchansk-at-triumf-dot-ca
Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3, Canada