Get Actual Disk Space

Question:

I am writing an application to copy files to a remote disk. I am using FileInfoToArray to get number of files and amount of space used. Then I use DiskFree to compute the amount of space available on the drive. If the total amount of space used by the files is less than the amount of free space, then I copy them. I am getting program errors of not enough room to copy the files. Am I missing something here?
; Setup file names to copy files2copy = StrCat(FilePath(logfile), FileRoot(logfile), "*.*") ; Get count and size of files to copy infoarray = FileInfoToArray(files2copy, 1|2) files2copycnt = infoarray[0,0] files2copysiz = infoarray[0,1] ; Ensure the files will fit onto the backup drive If files2copysiz < DiskFree("C:", 1) Then ((copy files, etc.))

Answer:

Yes, you are missing something. The size of a file and the space it takes on disk are two different things. Here is a short program that tells you the filesize and disksize of a file

; For standard NTFS volumes
moi=IntControl(1004,0,0,0,0) ; name of this wbt file
moisize=FileSize(moi)
dsize= ((moisize/32768)*32768)+32768
Message(moi,StrCat("Filesize=",moisize,@CRLF,"Disksize=",dsize))

In general, disk files are allocated on NTFS disks in multiples of 4096 bytes. Even if the file size is only 200 bytes, it takes 4096 bytes on disk. Other file systems, FAT and FAT32 have, in general, smaller blocksizes, so not as much disk spaces is wasted.

Think of say a 2 page printed memo. The first page is full and only 1/4 of the next page is used. You want to make 2 copies on the office copier machine. If you go my memo size ( 1 and 1/4 pages) and double it, you can figure you will need 2 and 1/2 pages to copy the memo. But when you do it, you find that you need 4 sheets of paper to copy the memo, because, typically, different memos cannot share one piece of paper.

The following function computes the cluster size on any volume. I've tested it on both NTFS and NWFS (NetWare) volumes, and the calculations are correct.

#DefineFunction ClusterSize_P6C ( pDriveLetter )
   ; David Gray / WizardWrx
   rClusterSize            = 0
   If VarType ( pDriveLetter ) == 2
      If StrLen ( pDriveLetter ) == 1
         SectorsPerCluster   = DiskInfo ( pDriveLetter , 1 )
         SectorSize         = DiskInfo ( pDriveLetter , 2 )
         rClusterSize      = SectorsPerCluster * SectorSize
      EndIf
   EndIf
   Return rClusterSize
#EndFunction

clstr_sz = ClusterSize_P6C ( 'c' )
Message( 'Cluster Size', clstr_sz )

Given the cluster size, calculating the space required on the volume is straightforward. Divide the file size by the cluster size, truncate the fractional part of the quotient, and add 1 for the fractional cluster.

Article ID:   W17032

File Created: 2007:07:03:14:27:42

Last Updated: 2007:07:03:14:27:42

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