Kevin Closson's Blog: Platforms, Databases and Storage

When file systems run out of space bad things happen. We like to investigate what those “bad things” are but to do so we have to create artificially small installation directories and run CPU-intensive programs to deplete the remaining space. There is a better way on modern Linux systems.

If you should find yourself performing Linux platform fault-injection testing you might care to add spurious space free failures. The fallocate() routine immediately allocates the specified amount of file system space to an open file.  It might be interesting to inject random space depletion in such areas as Oracle Clusterware (Grid Infrastructure) installation directories or application logging directories. Could a node ejection occur if all file system space immediately disappeared? What would that look like on the survivors? What happens if large swaths of space disappear and reappear? Be creative with your destructive tendencies and find out!

#include <asm/unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>


int main(int argc, char *argv[])
{
long int sz;
char *fname;
int ret,fd;

if (argc != 3)
{
fprintf(stderr, "usage: %s file new-size-in-gigabytes\n", argv[0]);
return(-1);
}

fname = argv[1];
sz   = atol(argv[2]);

if ((ret = (fd = open(fname, O_RDWR | O_CREAT | O_EXCL, 0666)))  == -1 ) {
perror("open");
return(ret);

}
if ( (ret = fallocate( fd, 0, (loff_t)0, (loff_t)sz * 1024 * 1024 * 1024 )) != 0 ){
perror ("fallocate");
unlink( fname );
}

close(fd);
return ret;
}

#
# cc fast_alloc.c
#
# ./a.out
usage: ./a.out file new-size-in-gigabytes
#
# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/sdc 2.7T 1.6T 1.2T 57% /data1
#
# time ./a.out bigfile 512
real 0m1.875s
user 0m0.000s
sys 0m0.730s
# du -h bigfile
513G bigfile
# rm -f bigfile
#
# ./a.out bigfile 512
# ls -l bigfile
-rw-r--r-- 1 root root 549755813888 Jul 1 09:48 bigfile