# lspv
hdisk0          00f6db0a6c7aece5                    None
hdisk1          00c0493045dbeb1e                    rootvg          active
#

• Here, hdisk0 is not active - this disk can safely be scrubbed or shredded.
• If you accidentally scrub or shred hdisk1, in this case, you destroy your running AIX in a faction of a second.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <strings.h>
#include <fcntl.h>

/* #define CORRUPT 1 */
#define BUFSIZE 64*1024*1024
char *buffer;
char *buffer2;

void write_file( char * filename)
{
    long writes=0;
    int fd;

    printf("write file %s blocksize=%d\n",filename, BUFSIZE);
    if( (fd = open(filename, O_WRONLY, 0)) == -1 ) {
        perror("failed to open file");
        exit(2);
    }
    while (    write(fd, buffer, BUFSIZE) == (size_t)BUFSIZE ) {
        writes++;
    }
    close(fd);
    printf("wrote %ld blocks\n",writes);
    sync();
}

void verify_file( char * filename)
{
    long reads=0;
    int fd;
    int j;

    printf("verify file %s blocksize=%d\n",filename, BUFSIZE);
    if( (fd = open(filename, O_RDONLY, 0)) == -1 ) {
        perror("failed to open file");
        exit(2);
    }
    while (    read(fd, buffer2, BUFSIZE) == (size_t)BUFSIZE ) {
#ifdef CORRUPT
        if(reads==4) buffer2[42]++; /* at block=4 byte=42 corrupt the data just read */
#endif
        for(j=0;j<BUFSIZE;j++) {
            if(buffer[j] != buffer2[j]) {
                printf("VERIFY FAILED at block=%d byte=%d as 0x%2x!=0x%2x\n",
                        reads, j, buffer[j], buffer2[j]);
                exit(24);
            }
        }
        reads++;
    }
    close(fd);
    printf("read %ld blocks\n",reads);
    sync();
}

void randomise()
{
int i;
    printf("prepare for phase random\n");
    for(i=0;i<BUFSIZE;i++)
        buffer[i]=(char)random();
}

void prepare(char ch)
{
int i;
    printf("prepare for phase 0x%02x\n",ch);
    for(i=0;i<BUFSIZE;i++)
        buffer[i]=ch;
}

int main(int argc, char** argv)
{
    buffer  = malloc(BUFSIZE);
    buffer2 = malloc(BUFSIZE);
    if(buffer == NULL || buffer2 == NULL) {
        printf("nshred malloc() failed\n");
        return 1;
    }
    srandom(getpid());
    if(argc != 2) {
        printf("nshred <disk-name>\n like nshred /dev/rhdisk999\n");
        printf("You must be the root user\n All disk data will be destroyed\n");
        exit(42);
    }
    if(strncmp(argv[1], "/dev/r",6)) {
        printf("nshred <disk-name> - disk name must start with /dev/r\n");
        exit(43);
    }
    prepare(0x55);
    write_file(argv[1]);
    prepare(0xAA);
    write_file(argv[1]);
    randomise();
    write_file(argv[1]);
    verify_file(argv[1]);

    return 0;
}

cc -O3 -o nshred64 nshred64.c

# lspv
hdisk0          00f6db0a6c7aece5                    None
hdisk1          00c0493045dbeb1e                    rootvg          active
#

# ./nshred64
nshred <disk-name>
 like nshred /dev/rhdisk999
 You must be the root user
 All disk data will be destroyed
# 

# time ./nshred64 /dev/rhdisk0
prepare for phase 0x55
write file /dev/rhdisk0 blocksize=67108864
wrote 512 blocks
prepare for phase 0xaa
write file /dev/rhdisk0 blocksize=67108864
wrote 512 blocks
prepare for phase random
write file /dev/rhdisk0 blocksize=67108864
wrote 512 blocks
verify file /dev/rhdisk0 blocksize=67108864
read 512 blocks

real    9m33.82s
user    0m7.72s
sys     0m4.47s
#

prepare for phase 0x55
write file /dev/r1GBFILE blocksize=67108864
wrote 512 blocks
prepare for phase 0xaa
write file /dev/r1GBFILE blocksize=67108864
wrote 512 blocks
prepare for phase random
write file /dev/r1GBFILE blocksize=67108864
wrote 512 blocks
verify file /dev/r1GBFILE blocksize=67108864
VERIFY FAILED at block=4 byte=42 as 0x70!=0x71