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Is it safe to de-fragment your disk when you have low disk space? What could be the consequences? What are the advantages and disadvantages of de-fragmenting. Is it possible to resume de-fragmentation of a disk after a few days? Can de-fragmentation of large disks be simplified as it takes lot of time to complete? Is it possible to lose data after de-fragmentation? Will it reclaim my Disk-space?

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" Is it Safe to De-fragment your Disk when you have low disk space, what could be the consequences?"

The defragmenter will not complete the defrag efficiently if you have low free space if you use the Windows defragger. But you can run a third party automatic defragger which defrags under less than 5% free space and get the job done without any problems.

"What are the Advantages and Disadvantages of De-fragmenting.Is it Possible to resume de-fragmentation of a disk after a few days. can De-fragmentation of large disks be simplified as it takes lot of time to complete. Is it possible to lose data after de-fragmentation. Will it reclaim my Disk-space."

There are no disadvantages, advantages are that the performance will be smooth and data access fast. With intelligent automatic defrag technology it's also possible to have a program defrag in the background without being resource intensive and will also defrag very fast as compared to the built-in program. Defrag doesn't create any new diskspace and there is no risk of data loss. Just ensure that you have a power backup for the PC.

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The most annoying consequence will be that defragmenting (since there will be files moved around) will be very slow and take a horrable amount of time. Advantages are, that your files are not fragmented on the harddisc and this will lead to a speedup unfortunatly with very low disk space the fragmentation effects increase dramaticly so that your hard disk will get fragmented again very fast and all defragmenting will be for nothing. There are some commercial programs who promise better results, but i can't tell you if they are any good. And to the last question: it will not recraim your disk space. The amount of free space will stay the same.

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Actually, because the hard disk is divided into 4K blocks it is possible to reclaim some space, because each fragment in a file can waste a small amount of space at the end of the fragment (up to 4K-1). But it's unlikely to be anything measurable. – Joel Coehoorn Aug 31 '10 at 17:01
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There is no risc for you. But the less space is available, the longer will the defragmentation need.

Defragmentation means: re-arrange the data on disk, so that (if possible) all the data in one file sits togetcher, physically on the disk. The if there will be a gain in disk space it will be very, very few bits..

Defragmentation can take a long time, depending on how large the amount of data /disk is and depending on the fragmentation found on the drive. You can stop and restart the defragmentation at any time in most defrag-tools.

Here a visualisation.. Imagine every char in the following ascii chart is a sector on the disk and a

  • "." means: free space
  • "+" means: file A
  • "*" means: file B

Here's your disk:

.+.++*..**+.*

The system will need to read at several addresses to get the content of file A! After defrag your disk looks like this:

++++..****...

Your system can now read file A or B without readjusting the physical needle on your disk.. so this will be faster.

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I only had defrag data loss one time in my life, it was because I had low disk space and tried to cancel the defrag because it was so slow, unfortunately it corrupted a critical system file, but like I said this only happened to me once in thousands of defrag routines. Defrag does not reclaim any disk space, it just consolidates the files on the hard drive. You need to do a disk clean up to gain disk space.

http://www.computerhope.com/issues/ch000528.htm

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If you find degragmentation to be a problem, you should do one of two things:

  1. Upgrade your operating system. Linux, but also Windows Vista and later don't fragment the disk as much, and Windows after XP automatically defragments whenever usage is low, so it doesn't waste your time.
  2. Get a solid-state disk (SSD). SSD's are truly random-access (like RAM) and don't ever need to be defragged.
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File systems fragment over time. SSD must not be defragmented because this will massively reduce their life time. – Mike L. Sep 1 '10 at 7:18
Correct. Also, they don't need to be defragged because on non-rotating media a fragmented file and a non-fragmented one can be read in the same amount of time. – CarlF Sep 1 '10 at 12:35
I'm not sure it's fair to say Vista and 7 fragment less. They do by default, however, defragment regularly of their own accord, which will lead to a perceived smaller amount of fragmentation. That is to say, they don't fragment less, they just defragment more often. – JBirch Sep 4 '10 at 0:58
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