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 Post subject: URPCs 21st Edition. Figure 9.13
 Post Posted: Fri Nov 22, 2013 8:56 pm 
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Scott, can you post an image for this figure? Looks like figure 9.14 got used instead.

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Fri Nov 22, 2013 9:39 pm 
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Yes indeed, thanks for letting me know! Here is the correct figure 9.13:


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Fri Nov 22, 2013 9:47 pm 
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Thanks. That makes much more sense. I wasn't sure how the figure made that part of chapter's text makes sense with the other picture. That section of the chapter makes more sense when you take apart a HDD. Now to just look for a Linear voice-coil actuator and a Stepper motor actuator.

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Fri Nov 22, 2013 10:31 pm 
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Quote:
Now to just look for a Linear voice-coil actuator...

The most popular drive with that feature was the Seagate ST-4038: http://www.ebay.com/itm/181263056477

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...and a Stepper motor actuator.

The most popular drive with that feature (and perhaps the best selling drive of all time) was the Seagate ST-225: http://www.ebay.com/itm/111218945761


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Fri Nov 22, 2013 10:49 pm 
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Is that the stepper motor on the bottom right of the picture you linked to?

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Fri Nov 22, 2013 10:59 pm 
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Quote:
Is that the stepper motor on the bottom right of the picture you linked to?

Yes it is. And Figure 9.8 from the 19th ed. (the last one to have this figure) shows a drawing of what this looks like from the top with the cover removed:


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Fri Nov 22, 2013 11:21 pm 
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That looks fantastically less reliable. Sounds like it would be a real pain if you were doing data recovery and were dealing with a drive that had data written while in a drastically different temperature environment.

Looking at these different actuators made me think of something. What is actually causing the click in the "click of death". What is happening?

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Fri Nov 22, 2013 11:35 pm 
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Quote:
That looks fantastically less reliable.

There was a huge difference in reliability between stepper motor and voice coil drives, however the former could be pretty reliable if they were properly formatted and taken care of. By that I mean formatted in the position and temperature they would be used, and not changed from that position or temperature during operation.

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What is actually ausing the click in the "click of death". What is happening?

In most cases that is the sound of the heads recalibrating on a voice coil drive. Some drives would do periodic thermal recalibrations where the heads would seek from the outer cylinder to the inner and several intermediate cylinders, making a series of clicking noises in the process. If the drive was failing, this could happen over and over, causing the "click of death"... Scott.


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sat Nov 23, 2013 12:07 am 
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Quote:
If the drive was failing, this could happen over and over, causing the "click of death"...
Would the failing component in this case be the actuator arm or the platters failing to spin properly? Would it be possible to replace any parts at this level to make it work again?

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sat Nov 23, 2013 12:48 am 
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Defective components such as the logic board, heads, actuator and platters could cause this. In a data recovery situation where the information on the drive was worth several thousands of dollars, parts such as the logic board, heads and actuator could be replaced. If the platters were damaged then the information would be lost regardless of the budget. Scott.


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sat Nov 23, 2013 12:53 am 
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Given the right equipment can't you still retrieve data from the undamaged parts of the platters? Wait, scratch that. If you replaced the parts you mentioned then you'd just have an HDD with "bad sectors" at that point, correct?

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sat Nov 23, 2013 1:13 am 
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As long as the platters were undamaged you could technically replace all of the other parts and retrieve the data. Since data is written by cylinder, head and sector, even if one platter were damaged virtually no usable data would be recoverable. Scott.


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sat Nov 23, 2013 1:31 am 
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So a head crash can cause serious and irrevocable damage? And also if you take about an HDD and see physical scratches across an entire platter then all is probably lost?

I assumed that each platter could be salvage regardless of the others. I understand that the actuator heads all work together but are you saying that if a bad sector is found by one head then all sectors above and below (on other platter surfaces) are tied to that bad read? For instance, in a drive with 3 platters that has one bad sector the drive would effectively "map" 6 total bad sectors? One for each surface (cylinder)?

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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sat Nov 23, 2013 12:06 pm 
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Quote:
So a head crash can cause serious and irrevocable damage? And also if you take about an HDD and see physical scratches across an entire platter then all is probably lost?

Yes and yes.

Quote:
I assumed that each platter could be salvage regardless of the others...

The platters are written in an interleaved fashion. Let's assume a drive with 2 platters, which would also mean 4 sides with 4 heads to write on them. A file that starts on Cylinder 10, head 1, sector 1 would then continue to be written on all of the remaining sectors on that track (a variable number on modern drives), then it would continue to be written on Cylinder 10, head 2 (the other side of the same platter), sector 1 (and all of the remaining sectors on that track, then Cylinder 10, head 3 (the first side of the 2nd platter), and so on. Losing one side of one platter would be like losing unevenly spaced and sized pieces of every file on the drive large enough to fill multiple tracks. In that case any small files that did not span the damaged platter could be recovered, and larger ones that were not binary could perhaps be partially recovered. For example if you had written a 100 page book in a text file you might get it back missing pages 10-20, 30-40, 50-60, etc. But for the most part any file missing pieces like that would be useless, especially binary ones.

Unfortunately when a head crash (platter damage) does occur, even if it was originally limited to one head (side) the resulting debris kicked up rapidly spreads throughout the drive potentially causing damage to most if not all of the other platter sides as well. The potential for this damage becomes greater the longer the drive is left running after the initial incident. Scott.


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sun Nov 24, 2013 11:33 pm 
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Quote:
The platters are written in an interleaved fashion...
That break down makes complete sense. I was thinking of a file being written sector by sector and then track by track then when that side of a given platter is full then moving to the next head. That would be insanely inefficient though...but better for data recovery. I suppose that's do to viewing drive info in disk defragmenting programs in a linear perspective.

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Unfortunately when a head crash (platter damage) does occur, even if it was originally limited to one head (side)...
Does that actually happen? I don't see that happening very often since the heads are all attached to a "single" (although multi-tiered) rigid actuator arm?

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...the resulting debris kicked up rapidly spreads throughout the drive potentially causing damage to most if not all of the other platter sides as well.
I take it the enclosed filter isn't designed to really handle that debris?

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sun Nov 24, 2013 11:56 pm 
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Quote:
I don't see that happening very often since the heads are all attached to a "single" (although multi-tiered) rigid actuator arm?

It may not happen often, but even though all of the heads are attached to the same actuator a head crash normally starts with only one of them.

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I take it the enclosed filter isn't designed to really handle that debris?

Not even close. Scott.


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Sun Nov 24, 2013 11:58 pm 
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Looks like SSD technology is looking better and better. Assuming price isn't an issue.

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Mon Nov 25, 2013 12:06 am 
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I miss having a laptop that ran off an SSD. Even if was dropped there was no worry of a head crash. Much more reliable and faster to boot. (no pun intended)

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Mon Nov 25, 2013 12:15 am 
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Price is most definitely an issue. However for my primary working system main drive I have only been using SSDs for a couple of years now. I still use standard HDDs for everything else though, including servers, backups, and all other non-primary systems. Scott.

PS: Don't misinterpret shock resistance for reliability. SSDs have their own reliability problems, and when they go, there is little if any data recovery possible. I must again mention BACKUPS as your only alternative to losing everything!


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Mon Nov 25, 2013 12:24 am 
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Quote:
PS: Don't misinterpret shock resistance for reliability. SSDs have their own reliability problems, and when they go, there is little if any data recovery possible.
I know what you mean (Trim, garbage collection, staying below 50% capacity, etc...). When I advocate for SSDs I put heavy emphasis on expected capacity (similar to HDDs but for performance reasons not based around default MFT size) and opting for a MLC drive instead of the cheaper (and not often obviously listed) TLC drives.

Evan


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Tue Nov 26, 2013 6:39 am 
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Hi Scott

Scott wrote:
Unfortunately when a head crash (platter damage) does occur, even if it was originally limited to one head (side) the resulting debris kicked up rapidly spreads throughout the drive potentially causing damage to most if not all of the other platter sides as well. The potential for this damage becomes greater the longer the drive is left running after the initial incident. Scott.

Could this be the reason drive failure is likely after bad sectors appear?


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 Post subject: Re: URPCs 21st Edition. Figure 9.13
 Post Posted: Tue Nov 26, 2013 6:34 pm 
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Yes indeed, especially if those bad sectors were caused by shock (head to platter contact). Scott.


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