hard disk integrity check
alan at linuxholdings.co.za
Sun Apr 16 23:30:47 UTC 2006
On Monday 17 April 2006 00:22, Yorvik wrote:
> Gary W. Swearingen wrote:
> > I'll propagate a rumor I heard: Use of "badblocks" has been
> > obsolete since drives started to remap their own bad blocks many
> > years ago. You won't find bad blocks until after your drive has
> > found so many that it's better used as a doorstop.
> > I beg to be corrected by someone with real knowledge.
> I was told a couple of years back, that if you can find bad blocks
> with 'normal user software' the drive has had it and may as well be
That's not true. There's many urban myths surrounding disks, and this
is one of them.
> Personally, I can remember when harddisks had labels on them
> listing the bad blocks.
Those were MFM drives. Drive manufacturers soon got fed up with the
support calls from users as to why they shipped faulty disks - ALL
drives have errors. Solution - disguise the errors. Modern drives
keep a small percentage of space free for bad blocks and as the
firmware picks up failing sectors, it remaps their location into this
unused space. The whole cyclinder/sector scheme is a pure abstraction
anyway, so this works well.
When you run badblocks and pick up a few errors, all you are doing is
beating the drive firmware to the same job. When you find it with
user software, it means that the firmware has given up trying.
Reading and writing to a disk is a tricky job (almost but not quite
entirely unlike reading and writing to RAM), and the firmware is
limited in what it can get the heads to do. The end result is that it
gives up easily, which opens up a nice market for third party
software. This is most of what disk data recovery is about. Spinrite
is a good example and http://www.grc.com explains it all nicely as
long as you can read past Steve Gibson's hyped opinions.
What you should be worried about is the *rate* at which bad sectors
are being produced. Once this passes a certain well-defined amount,
then the drive is becoming statistically more likely to fail. This is
what SMART is all about.
So while what you were told is not completely wrong, it's over
simplified by a very big margin
If only you and dead people understand hex,
how many people understand hex?
alan at linuxholdings dot co dot za
+27 82, double three seven, one nine three five
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