I write 1 program to create sparse file which contains alternate empty blocks and data blocks. For example block1=empty, block2=data, block3=empty .....
#define BLOCK_SIZE 4096
void *buf;
int main(int argc, char **argv)
{
buf=malloc(512);
memset(buf,"a",512);
int fd=0;
int i;
int sector_per_block=BLOCK_SIZE/512;
int block_count=4;
if(argc !=2 ){
printf("Wrong usage\n USAGE: program absolute_path_to_write\n");
_exit(-1);
}
fd=open(argv[1],O_RDWR | O_CREAT,0666);
if(fd <= 0){
printf("file open failed\n");
_exit(0);
}
while(block_count > 0){
lseek(fd,BLOCK_SIZE,SEEK_CUR);
block_count--;
for(i=0;i<sector_per_block;i++)
write(fd,buf,512);
block_count--;
}
close(fd);
return 0;
}
Suppose, I create a new_sparse_file using this above code.
When I run this program, on ext3 FS with block size 4KB, ls -lh shows size of new_sparse_file as 16KB, while du -h shows 8 kb, which, I think is correct.
On xfs, block size of 4kb, ls -lh shows 16KB but du -h shows 12kb.
Why are there different kinds of behavior?
If I increase the block_count to be written so that a 200MB file is created, on XFS du -h shows 187MB and on EXT3 it shows 101MB.
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