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Robin R Probyn

HDD question

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Never heard this before.. but recently someone told me (he had been told by someone else) that using a HDD over 50% capacity made them less reliable .. seemingly because the "arm" has to go out further to reach data on the outside of the disc.. I heard that data rates can change depending on where data is on the disc.. but never anything about reliability ..??

 

Thanks

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I am not aware of reliability problems, though a local data recovery lab has told me that spinning disks can suffer reliability problems reading and writing large files associated with video. because the head is intended to switch from read to write... if it maintains eaither state it can suffer crosstalk on written blocks and also demag the head.... or simply over heat the arm motor (like how clipping a speaker wears it out)

Also spinning disks are like records... they start on the outside edge... so full disks will have the arm close to the spindle... but the disk motor will have to work harder to maintain performance... that motor could fail... the spinof the disk is critical to keeping the head off the platter so of the motor fails it could allow the head to bounce along the platter smashing your bits to bits... creating dust which will cascade the problem.

Solid state disks take a reliability hit with lots of wrting... because SSDs have a limited number of 'writes' to each block... so they should be more reliable with read heavy applications.

but generally... hard drives fail... thats what they do in the long run. To quote a friend "If you're data isn't backed up twice, you dont have it."

Edited by Sam Javor

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Thanks for your reply.. yes I know HDD can fail :) .. they don't really need to work for that long for me.. just down loading footage on location and once into the edit..

 

But interesting I didnt know they recorded from the outside towards the centre.. in which case the only record to 50% would be totally bogus as the first 50% would be on the outside of the disc.. the area that supposedly creates the un reliable ness of any HDD.. according to what he was told anyway.. !

 

Is that true of all HDD.. fro outside to centre..

 

Thanks

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HDDs don't technically suffer a loss in reliability when nearly full. The problem arises when the disk begins to fill up, it causes the arm to seek across the platter sporadically causing increased wear and tear. You see, data is not necessarily written to contiguous sectors of the disk. This can leave gaps between full and empty sectors. The drive will attempt to write files in a contiguous fashion until there is not a large enough gap in free space. As the drive nears capacity, the drive must now break larger files into small non contiguous sectors, leading to an increasing amount of arm travel.

Imagine a 12 inch ruler, suppose you were to assume each inch was a sector of data and your finger was the arm. Now if you were to read from one to five, your finger would travel 5 inches. Suppose now you scrambled the numbers and tried to read one through five. Your finger could have traveled several feet depending on the positions of the days. Multiply that by thousands and you can imaging the extra work your HDD is doing.

 

This becomes less of a problem when writing large files like video because they tend to stay contiguous unless you reach the very limits of your capacity. To suggest that anything more than 50% capacity hams the drive is ludicrous. The max limit for me is around 85%-90%.

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There's an enormous amount of misinformation on this subject. It's like memory effect in NiCd batteries in that some of the described effects are real, but only apply in minutely specific circumstances, and are very rarely the real cause of reported problems.

 

Disks do not become less reliable when nearly full, or at least not significantly. They do sometimes become slower when nearly full, but again, absent other concerns, not significantly.

 

The issue is that there almost always are other concerns, mainly fragmentation, the effect that Louis describes. This occurs when files of various sizes are written and deleted as a disk is used. Beyond that, hard disks are mechanical devices and subject to wearing out.

 

Almost all of the effects in hard disks assumed to be caused by various highly specific and esoteric usage patterns are actually caused by either fragmentation, which is repairable, or wear and tear, which is not. A disk is most likely to be fragmented when it's full or nearly full in most usage scenarios. A disk is more likely to be full when it's old than when it's brand new. In neither case is the performance or reliability problem actually caused by capacity issues.

 

P

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There's an enormous amount of misinformation on this subject. It's like memory effect in NiCd batteries in that some of the described effects are real, but only apply in minutely specific circumstances, and are very rarely the real cause of reported problems.

 

Disks do not become less reliable when nearly full, or at least not significantly. They do sometimes become slower when nearly full, but again, absent other concerns, not significantly.

 

The issue is that there almost always are other concerns, mainly fragmentation, the effect that Louis describes. This occurs when files of various sizes are written and deleted as a disk is used. Beyond that, hard disks are mechanical devices and subject to wearing out.

 

Almost all of the effects in hard disks assumed to be caused by various highly specific and esoteric usage patterns are actually caused by either fragmentation, which is repairable, or wear and tear, which is not. A disk is most likely to be fragmented when it's full or nearly full in most usage scenarios. A disk is more likely to be full when it's old than when it's brand new. In neither case is the performance or reliability problem actually caused by capacity issues.

 

P

It is quite correct that many of the alleged disc faults are simply caused by excessive "thrashing" as the read and write heads are continually doing a "hunt-and-peck" job to reassemble all the data into the required contiguous stream for playback, or pigeonholing the data packets into widely scattered blank sectors.

 

You should always start every day with a freshly formatted drive, mechanical or solid-state, and iny case, simply bulk-copying a fragmented drive onto a freshly formatted one will fix a lot of those problems like magic.

 

For some reason people often seem to think they should use the original disc for an edit source and keep the backup for er, backup. That might be how it worked with film and videotape, but with digital recording, it's the other way round: Your "backup" is far more likley to be edit-friendly than the "original".

 

Regarding disk reliability, most of the problems seem to be related to transport and handling. For about 5 years I had a setup with six low-cost Digital Set-top boxes with inexpensive 500GB portable USB hard discs, for doing lossless recordings of Digital TV transmissions, mainly to capture TV commericals for quality checking purposes. Because I never knew precisely when ads were going to be shown, I would simply let the things run for 12 hours or so at a time, and use a simple non-decoding editor to snip out the relevant parts of the Transport Stream.

 

All I can say is, despite God knows how many hours recording they did, I've never had a single failure, either in the the physical drive or the recordings themselves.

 

Yet I know of many people (mostly students) whose similar portable drives had a very short and buggy life, from being banged around in a knapsack. :rolleyes:

 

 

 

 

 

 

 

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