IO size for write()

Question

I am playing around trying to adjust IO sizes to see broken IO and to adjust for large IO size in my app..
truss data of my IO
480: open("/mnt/file", O_RDWR|O_CREAT|O_TRUNC, 037777777777) = 3
480: write(3, "\0\0\0\0\0\0\0\0\0\0\0\0".., 4194304) = 4194304
480: write(3, "\0\0\0\0\0\0\0\0\0\0\0\0".., 4194304) = 4194304
62.059582 16.185079 480 1 0x3000338ecc0 0 strategy device: 584115552256 block: 60396848 size: 1048576 buf: 0x30000a78340 flags: 34088209
306.154426 17.819569 480 1 0x3000338ecc0 0 strategy device: 584115552256 block: 60398896 size: 1048576 buf: 0x300035dcc00 flags: 34088209
test C code:
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
main(int argc, char **argv[] ) {
int fd;
int a;
long linesize, size, size2;
char *writeline;
char *file;
file = malloc(512);
if ( argc < 2 ) {
printf("Syntax Error: test_io <filename>\n");
snprintf(file, 512, "%s", argv[1]);
printf("press ^C to stop\n");
writeline=malloc((2097152*2));
bzero(writeline, (2097152*2));
if ( (fd = open(file, O_RDWR| O_CREAT|O_TRUNC)) == -1 ) {
printf("error opening testfile\n");
exit(1);
for ( a = 0 ; (size = write(fd, writeline, (2097152*2))) != -1 ; a++) {
if ( a == 100 ) {
close(fd);
if ( (fd = open("file", O_RDWR| O_CREAT|O_TRUNC)) == -1 ) {
printf("error opening testfile\n");
exit(1);
kernel config:
set maxphys=2097152
ssd_max.... is set to the same...
I do not use the md drivers so md_maxphys is not in play...
any ideas?

Answer 1

the ssd is both sd and ssd.. inside the sd.conf and inside the /etc/system...
the following below is a tnf report of the IO size of my process to show the kernel is breaking the IO down.
sorry i wasn't clear on this part..
62.059582 16.185079 480 1 0x3000338ecc0 0 strategy device: 584115552256 block: 60396848 size: 1048576 buf: 0x30000a78340 flags: 34088209
306.154426 17.819569 480 1 0x3000338ecc0 0 strategy device: 584115552256 block: 60398896 size: 1048576 buf: 0x300035dcc00 flags: 34088209