i created a 32KB chunk size 3 disk raid5. then write this disk with a
small code i wrote. i found that even i write it with 1048756 in unit,
which is multiple of stripe size, it still has a lot of read when seen
from iostat.
any idea? thanks!
i attached the code for reference.
[root@bakstor2u root]# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid5] [multipath] [raid6]
[raid10] [faulty]
md0 : active raid5 sdc[2] sdb[1] sda[0]
781422592 blocks level 5, 32k chunk, algorithm 2 [3/3] [UUU]
unused devices: <none>
[root@bakstor2u root]# ./write /dev/md0 1048576 1000
1048576Bytes * 1000 : 34.745MB/s
avg-cpu: %user %nice %sys %iowait %idle
0.00 0.00 17.17 82.83 0.00
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
hda 0.00 0.00 0.00 0 0
hdc 0.00 0.00 0.00 0 0
md0 8791.92 0.00 70335.35 0 69632
sda 605.05 387.88 35143.43 384 34792
sdb 611.11 323.23 35143.43 320 34792
sdc 602.02 387.88 35143.43 384 34792
sdd 0.00 0.00 0.00 0 0
sde 0.00 0.00 0.00 0 0
sdf 0.00 0.00 0.00 0 0
sdg 0.00 0.00 0.00 0 0
sdh 0.00 0.00 0.00 0 0
/*
* I need a small program to write in various mode.
*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
int size, cnt;
char *buf;
char *fn;
int fid, i;
struct timeval tv1, tv2, ttv1, ttv2;
double x;
int sync = 1;
int timing = 0;
unsigned long *t;
if (argc < 4) {
printf("%s <fn> <strip size> <strip count> [s/a [t]]\n", argv[0]);
exit(1);
}
fn = argv[1];
size = atoi(argv[2]);
cnt = atoi(argv[3]);
if ((argc >=5) && (argv[4][0] == 'a'))
sync = 0;
if ((argc >=6) && (argv[5][0] == 't'))
timing = 1;
if (timing) {
t = (unsigned long *)malloc(sizeof(double) * cnt);
if (!t) {
printf("fail to get mem for t\n");
exit(1);
}
}
buf = malloc(size * sizeof(char));
if (!buf) {
printf("fail to get memory\n");
exit(1);
}
fid = open(fn, O_CREAT|O_WRONLY|(sync ? O_SYNC : 0), S_IRWXU);
if (fid == -1) {
printf("open file fail\n");
exit(1);
}
gettimeofday(&tv1, NULL);
for (i = 0; i < cnt; i++) {
if (timing) {
gettimeofday(&ttv1, NULL);
write(fid, buf, size);
gettimeofday(&ttv2, NULL);
t[i] = (ttv2.tv_sec - ttv1.tv_sec) * 1000000 + ttv2.tv_usec - ttv1.tv_usec;
} else
write(fid, buf, size);
}
close(fid);
gettimeofday(&tv2, NULL);
x = (tv2.tv_sec - tv1.tv_sec) + ((double)(tv2.tv_usec - tv1.tv_usec))
* 0.000001;
x = ((double)(size * cnt) / 1048576.0) / x;
printf("%8dBytes * %8d :%10.3fMB/s\n", size, cnt, x);
if (timing) {
for (i = 0; i < cnt; i++) {
printf("%8ld", t[i]);
if (!(i % 10))
printf("\n");
}
printf("\n");
}
}
