defraging? please explain

[johnno124]

i am not too sure about whether its safe to defrag or not.

Waht does it do?

will i lose my data?

[Ryoku]

it doesn't delete anything it just reorganizes to read the data more efficiently.

[DXMember]

 

[vanished]

It's safe (and considered routine maintenance) if you have a HDD.  If you have an SSD, do not do it - it will wear it out and give you no benefit whatsoever.

[mariushm]

When a file is created on the disk, the operating system tries to find a place on the drive with as much continuous space as possible and that's where the file is created. As data is written to the file, if some other file is in the way of the data being written, the operating system just makes a note there that says something like "if you want to continue reading data from this file, jump to this other place on the hard drive and continue reading from there" and the operating system finds another empty space on the drive as big as possible and continues writing data of that file there.  So a file is not necessarily one continuous block of bytes on the hard drive, it could be spread all over the drive in lots of small chunks.

 

An application that defragments the drive simply takes all the files from the computers, categorizes them in several degrees of importance and tries to put the most important files at the beginning of the hard drive, because it takes the smallest amount of time to read files from the beginning of a classic hard drive, and the read speed is the fastest there.

At the same time, if a file is split on the hard drive in lots of small chunks, the application is smart enough to join all those small blocks into one big block when the files are rearranged on the hard drive.

 

With SSD drives, all this is irrelevant, because no matter where data is on a SSD, the speed is the same and it takes the same amount of time to read data from anywhere on the SSD. In fact, in order to keep the flash memory chips at the same degree of  "wear and tear" (yes, memory chips have a finite lifetime, a limited number of bytes written to each memory chip), the controller chip inside SSD drives doesn't really write the data exactly where the operating system says so, but it actually spreads the data all over the memory chips trying to keep the number of writes in each memory as equal to the other chips as possible. 

 

So if you were to defragment a SSD drive, when the application says "hey SSD, I want to move this file to the beginning of the drive" the SSD will say "ok application, the file is created at the beginning of the drive" but in reality it will just pick a random memory chip and write to that random memory chip. So basically, you're wasting the SSD with a pointless operation.