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TOPIC: How many bad sectors is reasonable before a drive should be replaced?

How many bad sectors is reasonable before a drive should be replaced? 16 Sep 2017 15:19 #8567

I have an 2008 iMac that I brought out of storage. It had not bee heavily used and sat in storage for a couple of years. I installed 10.11 on it and it ran fine for a week or so. Then it froze up and wouldn't reboot. The fchk routine failed. I booted it with my TTP flash drive. The repair function in Disk Utility failed. Volume rebuild in TTP failed. So I am doing a disk scan. It is a 250 gig disk and has 488,000,000 blocks. After 14 hours, it has scanned about 178,000,000 and has found over 2000 bad blocks so far. I noticed that they tend to come in groups with the first big bunch around 545,000, then another big bunch at 1,200,000, etc. If the current rate holds, it will find around 5000 bad blocks. Is that a reasonable amount or is that an indication that the drive is failing?
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How many bad sectors is reasonable before a drive should be replaced? 16 Sep 2017 15:45 #8568

The forums are moderated. New postings do not appear until they are approved by a moderator. I have deleted your other posting with the same content.

In general, if there are more than just a few unremapped bad blocks detected by the Surface Scan, the drive should be replaced.

A few weeks ago, I had eight bad blocks detected by the Surface Scan on my internal hard drive. This was a very suspicious event, because the iMac (mid-2010) containing the drive had just had an improper shutdown as a result of too much virtual memory being in use. The Surface Scan in Checkmate had run recently, and no bad blocks were found. The drive, a new HGST rotational drive, flagged all of the blocks that were involved in reading or writing at the time of the improper shutdown as "pending bad blocks". The pending bad blocks showed up in the SMART data provided by our new Drive Scope S.M.A.R.T. utility. The drive itself checked the pending bad blocks later. Then Drive Scope showed no pending bad blocks, and that no blocks had been remapped to spares. So, I concluded that the pending bad blocks were not really damaged. A second run of the Surface Scan showed no bad blocks. If the blocks had been remapped to spares, they would not be detected as bad by the Surface Scan, but we know from Drive Scope that they were not remapped. HGST tech support emphasized, without giving details about why this is the case, that with relatively recent drives (both rotational and solid state), it is very important to avoid improper shutdowns.

I think it is fair to say that it is unlikely that over 2,000 blocks were flagged as pending bad blocks by your drive, and that the drive should be replaced.
MicroMat Inc
Makers of TechTool
Last Edit: 16 Sep 2017 16:03 by micromattech3.
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How many bad sectors is reasonable before a drive should be replaced? 16 Sep 2017 15:51 #8569

You can also check the Current Pending Sectors using the SMART test in TechTool Pro (as shown in the third screen capture, h3d7b31d.png, SMART attribute 197). The Reallocated Sectors count can also be checked in the SMART test in TechTool Pro (SMART attribute 5).

Here are some screen captures showing the situation with the internal HGST drive when it had pending bad blocks:
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MicroMat Inc
Makers of TechTool
Last Edit: 16 Sep 2017 16:12 by micromattech3.
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How many bad sectors is reasonable before a drive should be replaced? 16 Sep 2017 16:00 #8570

Here are some screen captures showing the situation with the internal HGST drive after the drive resolved the eight pending bad blocks:
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MicroMat Inc
Makers of TechTool
Last Edit: 16 Sep 2017 16:14 by micromattech3.
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How many bad sectors is reasonable before a drive should be replaced? 19 Sep 2017 03:58 #8591

Thanks for the tips. The drive failed the surface scan after 20 plus hours, so I have ordered a replacement.
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How many bad sectors is reasonable before a drive should be replaced? 19 Sep 2017 10:10 #8592

You are welcome, and I hope the new drive installation goes well.
MicroMat Inc
Makers of TechTool
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