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How many bad sectors does it take.......


Don W
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I was just wondering what the general consensus is regarding bad sectors. I bought four 3TB WD Reds and had them in a raid 5 for about a year and had noticed when I used the RocketRaid web interface that I had 1 bad sector. Well fast forward a year and I still have 1 bad sector so I tried WD's diagnostic tool and it said everything is fine. Since then I have removed them from the raid card and am now using Drive Defender and Home Server SMART. Well now I keep getting an alert that my drive is in a pre-fail state and I need to replace it but WD will not replace it since according to their software it is fine. I made sure that there is not any irreplaceable data on the drive but am considering replacing it any way.

 

Any Thoughts???

 

Thanks

 

Don

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It's the rate at which the bad sectors increase in a relatively short amount of time is what worries me.

 

I've had a drive with a few baddies logged a year ago but never increased. I'd say it's still ok.

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Oh good, like I said, I had one bad sector from the beginning and it has never increased or have I had bad performance. I guess I'll just keep an eye on it for now.

 

Thanks Everyone,

 

Don

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Worst case here, I believe Ikon can confirm this... if you do the advance replacement, it shouldn't matter. if you're really paranoid.

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Worst case here, I believe Ikon can confirm this... if you do the advance replacement, it shouldn't matter. if you're really paranoid.

 

I believe the problem is WD won't replace the drive.

 

     That said, I concur with the not worrying about one sector, although (of course there is a "but" - there's always a "but") it largely depends on how your SMART is reading that. I think Drashna can confirm, that it is highly likely - in fact, expected - that hard drives will have some bad sectors. The manufacturer builds in extra space for those sectors to be reassigned.

     The difference is some SMART readers will report the reassigned sectors and will give you a current and a "max" value. The max value is where the ahrd drive is (more or less) unable to reassign any more sectors and thus data loss is expected. As long as they aren't increasing, and/or aren't near the max value it is not a concern.

     HOWEVER, some SMART readouts only display those sectors which were UNABLE to be reassigned - and that would be a significant concern.

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I believe the problem is WD won't replace the drive.

 

     That said, I concur with the not worrying about one sector, although (of course there is a "but" - there's always a "but") it largely depends on how your SMART is reading that. I think Drashna can confirm, that it is highly likely - in fact, expected - that hard drives will have some bad sectors. The manufacturer builds in extra space for those sectors to be reassigned.

     The difference is some SMART readers will report the reassigned sectors and will give you a current and a "max" value. The max value is where the ahrd drive is (more or less) unable to reassign any more sectors and thus data loss is expected. As long as they aren't increasing, and/or aren't near the max value it is not a concern.

     HOWEVER, some SMART readouts only display those sectors which were UNABLE to be reassigned - and that would be a significant concern.

Working at StableBit has definitely given me a lot of insight into this. :)

 

 

Yes, the "Reallocated Sector Count" is actually the disks ECC record of how many bad sectors have been reallocated automatically by the drive's firmware.

 

Any time you write to a bad sector (either by normal usage or forcing it via chkdsk /r), the drive tries to recover the sector on the disk. And if it can't, it remaps the location to a "spare" section on the disk. This happens normally, and invisibly usually. And as you've said, there is a large amount of built in extra space for this. 

 

Though the "max" usually isn't the max sectors available. It's usually a threshold. Once the disk approaches this threshold, it usually means that there is a physical defect on the platters. And that you should replace the drive before data loss occurs (if it hasn't already).  Same goes for rapidly rising values here. This means that a platter of section of it has developed a severe issue.

 

There is an "uncorrectable sector count" value here. This is for when the drive FAILS to remap the sector. This is a very bad thing. 

 

Here is the Wiki Link, with the information about the SMART attributes. Worth reading, IMO:

https://en.wikipedia.org/wiki/S.M.A.R.T.#ATA_S.M.A.R.T._attributes

 

 

But, ... shameless self-promotion here:

The reason I love StableBit Scanner is that the "surface scan" actually checks each and every sector on the drive. Making sure it's readable. The *reason* this is awesome is that it will a) identify these bad sectors that have failed to automatically remap, and offer to recover the data from them (chkdsk doesn't care much about this, and once it's remapped... since it's remapped it can't be recovered), and B) because it's reading all the sectors on the disk, it may trigger this automatic error correction in the SMART firmware, preventing the bad sectors from "appearing" and potentially damaging data.

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In some ways, I think of Stablebit Scanner as a mini SpinRite. The main difference that I see is that SpinRite does a lot more to try to recover the data from a suspect sector. The other major difference to me is that Scanner works full-time, whereas SpinRite has to be run off line.

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Ikon, I think that's about the best comparison here I've heard. And am flattered by it. :)

 

Though, I think the main differences are that we don't write to the disks ever (unless it's to recover files from damaged sectors, and that's with your explicit permission). That, and we try to maintain the disks health. The surface scan should help prevent bad sectors from occurring (well, force the disk to remap before they affect you).  

 

But, having both tools in your "arsenal" is an absolutely great idea. Both are worth their money.

 

 

And just to clarify, the "repair" function on StableBit Scanner attempts 20 (I think) different "head positioning profiles" to try and read the data. Once it does, it copies it to the location "you" have specified. After that.... we don't do anything else. It's up to the disk to "heal" itself naturally (write to that location which causes the firmware to remap). Though, as I said, a chkdsk /r will force this to happen. 

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