Logic in Disk Defragmantation & Disk Check

Question

What is the logic behind disk defragmentation and Disk Check in Windows? Can I do it using C# coding?

Devindevina

Disk defragmentation is a complex topic and specific to the underlying file system of the device that you're defragmenting. What exactly are you trying to accomplish? – Falk

Why would you do disk defragmentation in C# if you don't know the concept of it? – Toponymy

I am doing a system based application. I want to implement a Disk defragmenter and Disk Checker in it. – Devindevina

-1 : I have no words. Prajeesh could you say where you got the idea to do this? – Mirepoix

@Prajeesh: no, I give up. Someone please help this guy destroy his disks. – Mirepoix

If it's NTFS you're defragmenting you can access the Win32 APIs via a [Dllimport] of the NtfsControlFile function, documented here: technet.microsoft.com/en-us/sysinternals/bb897427.aspx – Chekhov

I dont understand Why this negative voting. Is there any thing wrong with my question? I dont know the answer of my question. If any one knows, I can study from there. Those who negative voted, please confirm if you know the answer of my question. – Devindevina

@Prajeesh: you have asked us for a gun, bullets, and instructions on how best to pull the trigger with the barrel in your mouth. Maybe you want that information for good and safe purposes, but if so, then you haven't said that here. You haven't said why you want to know ("a system based application"). I'm concerned for the safety of your hard disks. Take frequent full backups, and keep the installation media handy. – Mirepoix

@John Saunders: I feel you're the one that doesn't know anything about defragmentation. There are Windows APIs for defragmentation that are completely safe, and you'd have to try really hard to corrupt your hard drives using them. See my answer below.. – Blanchette

@legenden: way wrong about that, I know about those APIs, and they make it hard to corrupt the disk if you have a clue. I saw no reason to believe the OP did. – Mirepoix

@All: The OP didn't ask "how do I move around file parts using C# and check for file integrity" or "how do I tinker with the layout of the files" or "do I have the know-how to mess around with low-level filesystem routines." The OP simply asked if it was possible - @legenden's response is sufficient enough. The OP could have also insinuated that they merely wanted to query for fragmented files and then instruct the defragmentation API to optimize those files (which you can do via WMI or direct to API). There was no essence of sophistication in his post. – Rosinski

Answer 1

For completeness sake, here's a C# API wrapper for defragmentation:

http://blogs.msdn.com/jeffrey_wall/archive/2004/09/13/229137.aspx

Defragmentation with these APIs is (supposed to be) very safe nowadays. You shouldn't be able to corrupt the file system even if you wanted to.

Commercial defragmentation programs use the same APIs.

Blanchette

Answer 2

Look at Defragmenting Files at msdn for possible API helpers.

You should carefully think about using C# for this task, as it may introduce some undesired overhead for marshaling into native Win32.

Croydon

Answer 3

If you don't know the logic for defragmentation, and if you didn't write the file system yourself so you can't authoritatively check it for errors, why not just start new processes running 'defrag' and 'chkdsk'?

Chekhov

Answer 4

Mark Russinovich wrote an article Inside Windows NT Disk Defragmentation a while ago which gives in-depth details. If you really want to do this I would really advise you to use the built-in facilities for defragmenting. More so, on recent OSes I have never seen a need as a user to even care about defragmenting; it will be done automatically on a schedule and the NTFS folks at MS are definitely smarter at that stuff than you (sorry, but they do this for some time now, you don't).

Stillage

This article is very much helpful. – Devindevina

Answer 5

Despite its importance, the file system is no more than a data structure that maps file names into lists of disk blocks. And keeps track of meta-information such as the actual length of the file and special files that keep lists of files (e.g., directories). A disk checker verifies that the data structure is consistent. That is, every disk block must either be free for allocation to a file or belong to a single file. It can also check for certain cases where a set of disk blocks appears to be a file that should be in a directory but is not for some reason.

Defragmentation is about looking at the lists of disk blocks assigned to each file. Files will generally load faster if they use a contiguous set of blocks rather than ones scattered all over the disk. And generally the entire file system will perform best if all the disk blocks in use confine themselves to a single congtiguous range of the disk. Thus the trick is moving disk blocks around safely to achieve this end while not destroying the file system.

The major difficulty here is running these application while a disk is in use. It is possible but one has to be very, very, very careful not to make some kind of obvious or extremely subtle error and destroy most or all of the files. It is easier to work on a file system offline.

The other difficulty is dealing with the complexities of the file system. For example, you'd be much better off building something that supports FAT32 rather than NTFS because the former is a much, much simpler file system.

As long as you have low-level block access and some sensible way for dealing with concurrency problems (best handled by working on the file system when it is not in use) you can do this in C#, perl or any language you like.

BUT BE VERY CAREFUL. Early versions of the program will destroy entire file systems. Later versions will do so but only under obscure circumstances. And users get extremely angry and litigious if you destroy their data.

Ivo

Thanks Philips, This may give me a solution. – Devindevina

There are Windows APIs for defragmentation which are completely safe, and work on the NTFS file system. – Blanchette