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otnateos
20th August 2010, 11:45 AM
Hi there,

I am a bit confused about how palimsest (disk utility) reporting bad sector. So if anyone can give me more insight on how it works I really appreciate it.

My last update in Fedora 11 includes palimpsest and then suddenly I realised that there is bad sectors in my hard drive (Seagate 1.5T ST31500341AS). So I decided to buy new ones and install it on RAID with new Fedora 13 installation (Seagate 1.5T drives again).

Few weeks later after few crashes I looked at the SMART status of my new hard drives and one of them already got 1 bad sector. (yup tell me stupid for buying the same drives). So I ask seagate support trying to get warranty fixed up. They tell me to use Seagate Tools and do long test. Looking at the way it works I believe it is the same thing like smartctl long test. After 7 hours later, no error is displayed which pretty much I can't do warranty claim

I do research on bad sectors and some people says palimpsest is a bit extreme on reporting bad sector, but another argue that's what the SMART is reporting. There is also discussion about it that I can simply ignore the bad sectors if they are not growing since they can be reallocated to another spare section of the hard drive.

There is also article about if we write zero to the hard drive it will remove the bad sector if it is a logical bad sector. I do this to my original Seagate drive using Seagate tools and palimpsest now reporting there are 40 sectors

Normalised:100
Worst:100
Threshold: 36
Value: 40 sectors
The 40 was about 18 sectors (as long as I could remember since I forgot to check it before wiping out the hard drive).

So

how paranoia should i be with the bad sector report from palimpsest?
to how many bad sectors should I worry and completely ditch my hard drive?
Is it really possible to reset the bad sectors or retest them. if yes how to do it?


I really appreciate suggestions /comments or informations regarding bad sector and palimpsest.

If any of you wonder why I was still stubborn and getting Seagate after the trouble. I read an article about setting up Peta Byte storage by Backblaze and thought if they can put their trust on Seagate, why can't I. I guess I was wrong..... this may be my last purchase from Seagate

jpollard
20th August 2010, 12:49 PM
It used to be that you needed to expect about 12 permanently bad sectors on any
100MB disk.

ALL disks have errors. Most are defects during manufacturing and are remapped to
to good sectors during a factory burn in. On a 1 TB disk, I would expect that to be
somewhere around a 1-2000 bad spots.... but normally these would be invisible.

After usage of a disk for a time (months) a few more disk errors can show up - these
are also manufacturing defects, but not caught during factory burnin. These should
also be invisible (or nearly so) since they should automatically be remapped to
good sectors.

It is only after the remap area is totally used up that errors start to be an issue.

Sometimes, a low level reformat can reclaim some bad spots - they are still weak,
but will not be a problem until sometime later. Unfortunately, reformatting wipes out
the bad sector list, so they must be located again. It is possible that your sudden
increase in bad spots is from re-discovering the spots that the manufacturers burn
in test recorded.

I haven't had to do a low level format in about 15 years. Most of those while using
Seagate drives. It is possible for a manufacturing run of bad drives... (anybody can),
but Seagate has had a good manufacturing reputation for most of that time.

BTW, writing 0s to a disk is just writing blocks of data. What it does is validate the
data blocks - any errors that are identified should be automatically remapped (unless
the disk has started failing...). You can try writing 0s again, just to see if MORE errors
occur. If it does, then I might start thinking the disk is failing...

JEO
20th August 2010, 01:10 PM
It is noteworthy to mention that the new version of palimpsest disk utility that comes with Fedora 13 is much less alarmist than the old Fedora 11 version. I have one 250GB drive that has 6 reallocated sectors and in that palimpsest shows a green dot and says "disk has a few bad sectors". As long as the number of bad sectors is not increasing over time I wouldn't worry about it.

otnateos
20th August 2010, 10:48 PM
thanks guys for the reply

I think i was just a bit paranoia the last bad sector i had was years ago before 1 GB came out.

Yes Fedora 11 was less forgiving speciall y with the notification. That's how i found out about the bad sector