Hi,
I am very interested in everything HDD-related, and currently reading a lot of information about how the HDD works and data recovery.
I am going to ask is for knowledge only, I know very well this drive won't live for long and I don't store anything important on it.
So I have this drive, previously pulled out of a laptop and used in an external USB3 case.
a month after I began using the drive in the case, I noticed a strange behavior so I checked SMART and there were 60 reallocated sectors.
after a long (windows) format, there are 218 reallocated sectors and (wow!) 65535 pending sectors.
I have a few questions:
1.when I write to the drive, the speed is 70-30 MB bus sometimes it drops to a stable 1.07MB/s. it will stay at that speed for a minute and then go back to higher speed, and vice versa.
Now I have noticed something weird, when I pick up my drive or gently shake it while the speed is 1.07MB/s, it will immediately restore high write speed. When I listen to the drive, it makes regular seeking sound while at the high speed, but when it goes to 1.07MB/s the sound changes to what I could best describe as "something is stuck in there and trying to go loose", that something I would presume is the heads. But it's strange since the writing still goes on, if the heads are stuck how could it still write anything? What could cause it to happen and for gentle movement to "fix it"?
2.While using the external case there were a lot of times when the drive lost power due to not too tight USB cable, could this have caused the bad sectors (maybe a minor head crash?).
3. how could I "force" the drive to reallocate the bad sectors? since windows (non quick) format didn't do it for all of them.

I am sorry if the post is too long, and I thank anyone who could spare some time to teach me the basics

@romitkin

It sounds like the drive maybe developing bad sectors and it's likely in it's last days. However, a 640GB drive has over a billion sectors on it so 65,535 potentially damaged sectors is really not very many in the grand scheme of things. Having said that, I would certainly not save any important data to the drive unless you have it backed up elsewhere. If the drive seems to have a slight problem with the USB connection, that could be related to the reasons it seems to pick up write speeds when you move it around a little. As far as stuck heads goes, it's true.... When the heads are stuck, the platters will not spin and there will be no more reading and writing data to the platters. Hard drive's naturally make searching sounds as they are in operation so that could be the sounds you are hearing.

It is possible that the drive suddenly losing power has caused light head crashes and is the cause of the bad sectors. The hard drive's firmware will automatically re-allocate the bad sectors automatically if it can. Otherwise, you have to have access to a more powerful hardware based tool that will allow you to manually re-allocate those bad sectors. We use PC-3000 UDMA from Ace Labs to allow us to work directly with the firmware. It's a very complicated tool that takes years to master but the capabilities are amazing.