Creating a contiguous file

[GrosM]

Hello everyone !

I love this utility, code is clear and gave me better understanding of how to control fragmentation on my disk.
However, I'd like to go further by being able to create a file of a certain size, unfragmented. The only solution I found so far is to create the file, write my data and defragment it, which is indeed costly.
Does anybody knows if there are any system calls that can be used to allocate several contiguous clusters to a newly created file ? I looked up MSDN without any luck...

Thanks !

GM.

[GippleDocks]

I think Syinternals's contig utility with the '-n' parameter will do it.  See http://www.microsoft.com/technet/sysinternals/utilities/contig.mspx .

[GrosM]

Yes, that's what I'm doing now : launching the process "contig.exe" and then writing on it, but this process creation is rather slow compared to coding it myself. Besides, I'm not sure that it doesn't do the same : creating the file, fixing its length and defragmenting it.
I couldn't find the source code of Contig, I'm not sure it's open source but I'll check on it.
If someone has it though, I'd be interested !

Thanks !

[jeroen]

Does anybody knows if there are any system calls that can be used to allocate several contiguous clusters to a newly created file ?

Take a look at the FSCTL_SET_ZERO_DATA control code. It does not guarantee contiguous clusters, but since it is a very low-level function call it is extremely fast, and since you specify the size of the file it "knows" how big the new file must be, and can theoretically use that information to create a unfragmented file. I think it's the closest you can get to pre-allocating a file in Windows.

[GrosM]

Thanks, I'll give it a try if I have some time. It sound promising along with the registry key "ContigFileAllocSize".
Thank you !

[jeroen]

registry key "ContigFileAllocSize"

I didn't know that key! Sounds interesting. I wonder if it can be changed on-the-fly, or wether you have to reboot after changing it. Also I wonder which Windows versions support it, I haven't found any Microsoft docs. And I think you will get a disk full error if no gap is big enough, which may happen even though there is plenty of free space.

[GrosM]

From what I read on the Internet (as you said, no Microsoft documentation was found), you should change the value, defrag and reboot, which would make it not very dynamic.
If you know the average file size (and in my case, I know), you can set it up to decrease fragmentation. I have read that people put it at 0x200 (512 kb) and had great result with Windows XP.
I tried 0x1000 (4 Mb) on 2003 Server and it didn't work so fine. It seems that file fragmentation was low but directory fragmentation was very high.

[Myriades]

Hi all
i've found doc under microsoft technet ( windows 98 )

HKEY_LOCAL_MACHINE \System \CurrentControlSet \Control \FileSystem

An additional performance setting in the FileSystem subkey, ContigFile AllocSize, can be used to change the size of the contiguous space that VFAT searches for when allocating disk space. Under MS-DOS, the file system began allocating the first available space found on the disk, which ensured a great deal of disk fragmentation and related performance problems. By default under Windows 98, VFAT first tries to allocate space in the first contiguous 0.5 MB of free space and then returns to the MS-DOS method if it cannot find at least this much contiguous free space. This optimizes performance for both the swap file and multimedia applications.

In some cases, you might choose to set a smaller value in the registry, as when you are not running demanding applications on the computer. A smaller value for ContigFileAllocSize, however, can lead to more fragmentation on the disk and, consequently, more disk access for the swap file or applications that require larger amounts of disk space.

it seems that only vfat filesystem is concerned

[Astroman]

I use this computers I work on, and have for quite some time, part of my tweaks.

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem]
"NtfsDisableLastAccessUpdate"=dword:00000000
"NtfsDisable8dot3NameCreation"=dword:00000001
"NtfsMftZoneReservation"=dword:00000001
"ContigFileAllocSize"=dword:00000200

[Lexar]

Just happened to come across:
BizTalk Server Database Optimization

ContigFileAllocSize | Adjusts the minimum contiguous file allocation to 64KB; this is generally only for database servers, and should be used with great caution as it can cause servers with heavy small file traffic to quickly fill disks. On the positive side, it significantly reduces fragmentation of data files by forcing larger contiguous allocations.

Looks like it's not only for VFAT, though I am not sure if it works on WinXP.

[Lexar]

And to my chagrin, it didn't work on NTFS under Windows XP. I set the value to 1024(0x400), copied a small file and a somewhat larger file to another location and checked if they are less fragmented than 1024KB per fragment, to a disappointing result:

Code:

Bytes: 81276
Clusters: 20
Fragments: 5
File system: NTFS
Compressed: No
Modified: 10.12.2007 15:08

Code:

Bytes: 36668736
Clusters: 8953
Fragments: 53
File system: NTFS
Compressed: No
Modified: 10.12.2007 15:12

[jeroen]

it didn't work on NTFS under Windows XP.

Did you reboot after changing the setting?

[Lexar]

it didn't work on NTFS under Windows XP.

Did you reboot after changing the setting?

Yes, I did so. It didn't work on NTFS under plain Windows XP Home Edition.

Looks like I will still need your JkDefrag v4.0 very much.(^^)

[controller]

i found out there are two of these "ContigFileAllocSize" registry entries

Code:

Windows Registry Editor Version 5.00

; set ContigFileAllocSize to 64Kb
; one for w98 and one for winxp

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem]
"ContigFileAllocSize"=dword:00000040

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
"ContigFileAllocSize"=dword:00000040