[ale] disk drive diagnostics nirvana - NOT - I have questions

[Ron Frazier (ALE)]

Hi all,

I've spent the last couple of days doing disk diagnostics on all my hard 
drives, which I do periodically, and learning more than I really wanted 
to know about sector errors.  I'll try to share more details later, but 
for now, I'm just going to post the minimum.  As you may know, a HDD 
that works perfectly from the factory may develop problems over time and 
show either bad (reallocated) sectors or bad blocks.  Since the HDD 
controller can usually only discover read / write problems when you 
actually access the sector, I've developed a practice over the years to 
read and write every sector on the hard drive a few times per year.  I 
usually use Spinrite, which can operate on Windows or Linux drives.  It 
boots as a free standing executable.  In the mode I use, it reads, 
inverts and rewrites every sector on the disk, then does it again.  This 
forces the drive's controller to find and remap any weak sectors to 
somewhere else while they can still be read properly.  If the sector 
doesn't read, Spinrite uses advanced statistical algorithms to try up to 
2000 times to recover the data.  You can also do something similar with 
badblocks -nsv in Linux, except for the bad sector recovery, although I 
don't know exactly what algorithm it uses.  On a large drive, these 
tests take days to complete.  Once they're done, I know that the drive 
can absolutely read or write any sector reliably, or if it couldn't, 
those questionable sectors should have been reallocated to other areas 
by the controller.  The first thing I do when I get a new drive is write 
it with random data then Spinrite it about 6 times to thoroughly burn it 
in.  I then follow up with one such procedure every 4 - 6 months.

What usually happens is:

* Run file system check.  No problems, or minor problems fixed.
* Run Spinrite or badblocks.  No read write errors.
* Follow up by checking SMART data using Disk Utility or GSmartControl.  
(PS, Disk Utility will not show SMART data on a USB drive due to a bug, 
but GSmartControl can.)  No bad sectors and no pending reallocations.

I have two 1 TB drives that I use for backup.  I backup to one then 
mirror it to the other.  I recently had occasion to completely read one 
and write the other in a mirroring process.  As far as I know, there are 
no read or write errors.  When I ran the SMART check, I found that one 
of these has 12 bad or reallocated sectors and the other has 120.  This 
prompted me to start the Spinrite process on one, which I haven't 
finished, to read, invert, write, read, invert, write the data.  I could 
have used badblocks as well.  I've finished 72% of one drive, and, thus 
far, have had no read or write failures or bad blocks reported.

So, the $ 600,000 question is this.  Assuming every active sector on the 
drives can be successfully read and written, should I be concerned about 
12 or 120 bad reallocated sectors?  I find a wide variety of opinion on 
the net ranging from not a problem all the way to replace the drives 
immediately.  Note that these are my backup drives for this PC, so I 
REALLY don't want them to fail.  The drives may be more than 5 years 
old.  I'd have to dig through receipts.  However, they're showing a 
powered on time of 2.1 years.

Let me know what you think.

Any help, as always, is greatly appreciated.

Sincerely,

Ron



-- 

(To whom it may concern.  My email address has changed.  Replying to former
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Ron Frazier
770-205-9422 (O)   Leave a message.	
linuxdude AT techstarship.com