[ale] Which large capacity drives are you having the best luck with?

[Ron Frazier]

Hi Pat,

We're getting a little above my level of knowledge on hard drive
operation here, but here's my take on it.  A modern drive is always
generating read errors and relying on ECC to get you the right data.  It
can be readable enough, with difficulty, without generating an error
flag.  Therefore, they may not be flagged unless they get above a
certain threshold.  When Spinrite tries to read the data, if it has
difficulty above a certain limit, I believe it relocates the data
somewhere else.  This may or may not raise a flag in the smart system.
It also doesn't mean that the sector has been reallocated.  The
intensive analysis of Spinrite inverts the data and writes it back,
reads it, inverts it again to its original state, then writes it back
again.  This forces the drive's firmware to evaluate the performance at
that point, and forces the surface to absorb both a 1 and 0 in turn at
that point.  Also, I believe that the magnetic fields deteriorate over
time.  I could probably corroborate that with some extensive research.
Just anecdotally though, most of the files I've ever lost due to disk
malfunctions seem to be things that were almost never accessed except
rarely.  The read invert write read invert write cycle, if nothing else,
will ensure that all the magnetic bits are good and strong since they
are all ultimately rewritten.

There are basically 3 possibilities prior to running the diagnostic:

1) The drive has no serious (above threshold) errors either latent or
obvious. - In this case, every magnetic domain on the surface will be
refreshed, which is good, and will keep the read error rate as far below
the threshold limit as possible.  Also, the firmware will be forced to
evaluate the performance of every bit and byte.

2) The drive has latent errors but no warnings. - There may be areas
that are barely readable or that are not readable under normal
circumstances (but have never been attempted).  They will be read if
possible after extensive effort, and will be relocated to a different
part of the drive if needed.  This may or may not cause a sector
reallocation or generate any error messages.  Again, the magnetic fields
will be refreshed.

3) The drive has obvious errors and warnings. - In this case it is
likely that some data is unreadable by conventional means.  It is highly
likely that Spinrite will recover the data and save it elsewhere on the
drive, storing it in fresh strong magnetic domains.  Again, this may or
may not trigger sector reallocation.  Spinrite will report these data
areas as recovered or unrecovered as appropriate.  The drive itself may
still be fully usable, if, for example, the data error was caused by a
power failure, but the drive was not damaged.  If sectors start getting
reallocated, I would agree that it's time to consider changing the drive
out, as I did with one of mine last night.  Regardless, Spinrite can
often recover your data enough to boot the drive and get the data off
before decommissioning the drive.  The smart reporting screen of
Spinrite is somewhat hard to read, and I don't know if it reports sector
reallocation.  I would use the Ubuntu Disk Utility or gsmartcontrol /
smartctl as a final check to look for warning signs (now that I know
about it) even if Spinrite is happy.

I'm not suggesting that everyone has to use the product, just sharing
some info that I feel might be helpful.  I have found the product useful
in the past.  To each his own.

Sincerely,

Ron

On Wed, 2011-01-05 at 15:20 -0500, Pat Regan wrote:
> On Wed, 05 Jan 2011 11:23:47 -0500
> Ron Frazier <atllinuxenthinfo at c3energy.com> wrote:
> 
> > However, even if there are not obvious results, the intensive read
> > rewrite process will refresh weak data and improve the reliability of
> > the drive.  If data is unreadable, it will go to EXTREME measures to
> > recover it.  Even normal operations are slow.  It just so happens that
> > I'm running Spinrite at the moment on my Son's laptop with a 250 GB
> > drive.  I'm using the most intensive level of analysis.  It's almost
> > finished after 20 hours with no errors.  I think my hard drives are a
> > bit faster than my Son's.
> 
> If there are no read errors on a drive Spinright's rewrite cycle is of
> no use whatsoever.
> 
> Spinrite's rewriting exploits the fact that IDE and SATA drives will
> only relocate a bad sector on a write and not on a read.  SCSI and SAS
> drives will relocate a bad sector on a read, or at least they should.
> 
> Once a drive starts relocating sectors it is usually the beginning of
> the end of its useful like.  I don't trust data to drives that start
> showing read errors.
> 
> Hard drives are very cheap.  Your data is probably valuable.  
> 

-- 

(PS - If you email me and don't get a quick response, you might want to
call on the phone.  I get about 300 emails per day from alternate energy
mailing lists and such.  I don't always see new messages very quickly.)

Ron Frazier

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linuxdude AT c3energy.com