My os and drive is
OS: Windows XP sp2 or Linux SUSE 9 or Cygwin
Compiler: Visual C++ 2003 or Gcc or Cygwin
PC and os are both 32 bits
So, How can I create a super-huge file in secs
I was told to use MappingFile functions. I failed to create files over 2G So... Your warm responses will be all appreciated thanks
Using dd
in Linux to create a 1 gb file takes 57 seconds 'wall clock time' on a somewhat loaded box with a slow disk, and about 17 seconds system time:
$ time dd if=/dev/zero of=bigfile bs=G count=1
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB) copied, 53.9903 s, 19.9 MB/s
real 0m56.685s
user 0m0.008s
sys 0m17.113s
$
you can use dd
dd if=/dev/zero of=bigfile.txt bs=$((1024*1024)) count=100
or just plain shell scripting and contents doesn't matter
1) create a dummy file with a few lines, eg 10 lines
2) use cat dummy >> bigfile in a while loop
eg
while true
do
cat dummy >> bigfile.txt
#check for number of lines more than 10000 for example and break out of loop
done
Do another time
while true
do
cat bigfile >> bigfile2.txt
# check for size and break out..
done
rm -f dummy bigfile
Does the file have to take up actual disk space? If not, you could always (in Cygwin, or Linux):
dd if=/dev/zero of=bigfile seek=7T bs=1 count=1
This will create an empty 7 TB file in a fraction of a second. Of course, it won't allocate much actual disk space: You'll have a big sparse file .
Writing a program under Cygwin or Linux, you can do the same thing in a C program with a call to ftruncate .
Depending on your system limits you can create a largefile in a fraction of a second...
FILE *fp = fopen("largefile" ,"w");
for(int i = 0; i < 102400; i++)
{
fseek(fp, 10240000, SEEK_CUR);
}
fprintf(fp, "%c", 'x');
fclose(fp);
Play with this.
cat /dev/urandom >> /home/mybigfile
It will error out when disc space has ran out.
This is for linux/bsd/possibly cgywin
In suse in a VM I did dd if=/dev/zero of=file;rm file
which filled the disk, and when it was full deleted the file. This allowed me to compress the image a little more for some reason, and I read about doing it on a forum somewhere.
You can use "fsutil" command for Win2000/XP/7:
c:> fsutil file createnew Usage : fsutil file createnew Eg : fsutil file createnew C:\\testfile.txt 1000
Reagrds
If you want a sparse file you can do that also on Windows (on NTFS volumes), using CreateFile, DeviceIOFunction with FSCTL_SET_SPARSE and FSCTL_SET_ZERO_DATA; for more info see here .
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