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Old 08-21-2010, 12:22 AM   #1
sulekha
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Question HDD vs removable media ?


Hi all,



In a Hard disk ,The data platters are completely sealed so that no dust/dirt can get in this feature makes hard disk more reliable than removable media isn't it.
Is there any other feature that makes HDD a better proposition than removable media ?
 
Old 08-21-2010, 03:14 AM   #2
smoker
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Quote:
Originally Posted by sulekha View Post
In a Hard disk ,The data platters are completely sealed so that no dust/dirt can get in this feature makes hard disk more reliable than removable media isn't it.
Not really, it makes a hard disk more reliable than a hard disk that isn't sealed. CDs and DVDs have error correction and have no moving parts or electronics to break down. Solid state memory (flash) is similar and also in most cases faster.
Quote:
Originally Posted by sulekha View Post
Is there any other feature that makes HDD a better proposition than removable media ?
Larger capacity, faster RW speeds (than optical media), faster random access (but not faster than flash).
 
Old 08-21-2010, 07:52 AM   #3
onebuck
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Hi,

Quote:
Originally Posted by smoker View Post
Not really, it makes a hard disk more reliable than a hard disk that isn't sealed. CDs and DVDs have error correction and have no moving parts or electronics to break down.
I have never seen a hard disk that isn't sealed. Even early SMD drives had a sealed environment after the platter set was installed. No functionality until chamber was cleared. Then spin up and functional. Without a sealed environment then a head crash was imminent for a flying head assembly.

CD & DVD do have a carrier that moves the laser assembly. How do you think the read or writes are performed on the drives? No Electronics? If your speaking of the media then of course no circuitry but alignment via layer bit control that is burnt initially then readable via the laser photo array and circuitry within the device.

Quote:
Originally Posted by smoker View Post
Solid state memory (flash) is similar and also in most cases faster.Larger capacity, faster RW speeds (than optical media), faster random access (but not faster than flash).
Rather confusing statement above. You could clarify a bit. Solid-state drive(SSD)? RamDisk? Flash what? Flash memory or USB flash drive ?

 
Old 08-21-2010, 02:04 PM   #4
10110111
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Quote:
I have never seen a hard disk that isn't sealed.
Then you didn't look properly
In reality, almost no HDD is sealed. All of them have a 'breather hole' which has a filter behind it. This hole is needed to make pressure inside the HDD constant enough so that the spinning disk could make the head float above it with the needed distance.
Quote:
The data platters are completely sealed so that no dust/dirt can get in this feature makes hard disk more reliable than removable media isn't it.
Not much more if true at all. Try dropping an HDD from your table. In the worst circumstances HDD head will unpark and stick on the disk, having made a track of BADs on it. If the disk is on and you beat it with enough stress, you'll make the head bump into the disk, thus creating a series of BADs too.
So, i wouldn't say HDD is very reliable. I'd rather say this about SSD instead.

Last edited by 10110111; 08-21-2010 at 02:05 PM.
 
Old 08-21-2010, 02:17 PM   #5
ronlau9
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Quote:
Originally Posted by 10110111 View Post
Then you didn't look properly
In reality, almost no HDD is sealed. All of them have a 'breather hole' which has a filter behind it. This hole is needed to make pressure inside the HDD constant enough so that the spinning disk could make the head float above it with the needed distance.

Not much more if true at all. Try dropping an HDD from your table. In the worst circumstances HDD head will unpark and stick on the disk, having made a track of BADs on it. If the disk is on and you beat it with enough stress, you'll make the head bump into the disk, thus creating a series of BADs too.
So, i wouldn't say HDD is very reliable. I'd rather say this about SSD instead.
And if you drop you entire computer from you're desk ,you have a good change that will never work again.
You should handle this things with care .
 
Old 08-21-2010, 05:56 PM   #6
10110111
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Quote:
And if you drop you entire computer from you're desk ,you have a good change that will never work again.
You should handle this things with care .
I just said about reliability. Even if you through your flash stick out of the window on the 10th floor, chances are very high that your stick will still function. But drop HDD from 1m height, and most likely it'll have many bads. Of course, things should be handled carefully, but you never know...
 
Old 08-21-2010, 06:34 PM   #7
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Hi,
Quote:
Originally Posted by 10110111 View Post
Then you didn't look properly
In reality, almost no HDD is sealed. All of them have a 'breather hole' which has a filter behind it. This hole is needed to make pressure inside the HDD constant enough so that the spinning disk could make the head float above it with the needed distance.
Still a sealed environment via the inside filter and recirculation filters within the platter chamber. Doesn't breathe in the platter chamber since the air flow is generated by the platters in motion! The flow of air inside the chamber is filtered via the recirc filter The head is flying via aerodynamics above the platter. As for direct air flow in the disk area, no way. In older SMD there was the believe for the need of air flow. The spindle assembly for the platter will create the necessary flow for the head to fly above the platter . Hopefully the head never makes contact. The head assembly and the platter motion creates the flight action for the head.

Quote:
Originally Posted by 10110111 View Post
Not much more if true at all. Try dropping an HDD from your table. In the worst circumstances HDD head will unpark and stick on the disk, having made a track of BADs on it. If the disk is on and you beat it with enough stress, you'll make the head bump into the disk, thus creating a series of BADs too.
So, i wouldn't say HDD is very reliable. I'd rather say this about SSD instead.
A properly designed drive assembly will take typically 350G operating with a 1000G for non operation.

Only if the drive has accelerometers and electronics designed for such. Not all HDD will have this feature. Any mechanical shock could possibly cause a head crash during operation. Hopefully the user doesn't drop nor bang the system off the wall.

As for the SSD, cost vs storage here. Sure durable but at what cost? Density and volatility depends on the type of SSD then add the cost for the bigger units.

I believe a spinning HD is still a cheap means of large storage but a slow one compared to solid state based devices with smaller sizes. The density will change for the SSD along with the cost.
 
Old 08-22-2010, 04:42 AM   #8
10110111
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Quote:
Doesn't breathe in the platter chamber since the air flow is generated by the platters in motion!
You mean platter chamber doesn't exchange air with outside? Suppose you bring your HDD from outdoors with air temperature of -10°C to a room with 30°C inside. If the platter chamber had constant amount of air, then air pressure would noticeably increase, thus leading to more R/W errors because the head would fly farther from the disk.
Quote:
Originally Posted by wikipedia
Hard disk drives require a certain range of air pressures in order to operate properly. The connection to the external environment and pressure occurs through a small hole in the enclosure (about 0.5 mm in diameter), usually with a filter on the inside (the breather filter).
 
Old 08-22-2010, 05:10 AM   #9
smoker
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Quote:
Originally Posted by onebuck View Post
CD & DVD do have a carrier that moves the laser assembly. How do you think the read or writes are performed on the drives? No Electronics?
Since the discussion was about the media then obviously ! But the media itself has no moving parts. Unlike a hard disk which is a self contained device.

And as for the sealed/unsealed business, I was merely pointing out that sealing the drive is only relevant when compared to another hard drive, it is not an extra or defining point of reliability over removable media. And who ever said that the seal was airtight ?
 
Old 08-22-2010, 07:34 AM   #10
onebuck
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Hi,
Quote:
Originally Posted by 10110111 View Post
You mean platter chamber doesn't exchange air with outside? Suppose you bring your HDD from outdoors with air temperature of -10°C to a room with 30°C inside. If the platter chamber had constant amount of air, then air pressure would noticeably increase, thus leading to more R/W errors because the head would fly farther from the disk.
Your correct about the temp and pressure change within the chamber. And yes, the exchange for balance is through two filtration systems with the recirc isolating the platter chamber. The recirc isolates the the platter chamber from the drive chamber and breather filter. Pressure in the platter chamber is still controlled through the recirc filter and air flow is generated by the spindle & platter assembly.

No argument with the balance of pressure in the platter chamber but still not active air flow exchange. If so then the recirc filter would just re-introduce particles that had been filtered. These particles are from wear or even manufacture. It doesn't take a very large particle to cause a crash of the head & platter thus damaging the disk or head. The best analogy is a rabbit crossing a runway with a 747 flying 4 inches off the same runway. Something is going to happen when the 747 hits the rabbit.
 
Old 08-22-2010, 08:38 PM   #11
teckk
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To the OP

Hard drives are susceptible to magnet fields. A magnetic field can erase or corrupt data.
Hard drives have a limited life. There is a motor spinning and heads parking and unparking. I think 20 - 30k parks is the life of one. WD is having problems with their green drives dying early because the darn things park every few seconds if not reading. Drives either dye right away or last for years it seems. Subject to design change. PATA- SATA.

SSD's have no moving parts, should last, but are a bit expensive still.

Optical media is heat and scratch susceptible. They should last if kept in a good storage climate. CD-R, DVD-R are suppose to last for decades but that can't be proven yet. Plus the formats aren't lasting long enough to find out. 10 years ago we used CD-R. Now single layer DVD's are being replaced by double-quad layer and Blueray.

Flash memory is compact and handy. You can puts lots of data in a small space. It also has limited read write life. That's also susceptible to design change. USB is popular now but that could change.

I think if you have something valuable to store, put it on different media in different locations. Back it up on magnetic and optical or flash. The major problem about keeping data may not be the reliability of the media but rather the fast obsolescence of the hardware to use your media.
 
  


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