1048576 = 1024 * 1024 = 32 * 32768. :)
so it should be 32 stripe writes.
ming
On Fri, 2005-07-22 at 23:14 -0700, Tyler wrote:
> By my calculations, 1048756 is *not* a multiple of 32768 (32
> Kilobytes). Did I miscalculate?
>
> Regards,
> Tyler.
>
> Ming Zhang wrote:
>
> >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");
> > }
> >}
> >
> >
> >
> >------------------------------------------------------------------------
> >
> >No virus found in this incoming message.
> >Checked by AVG Anti-Virus.
> >Version: 7.0.323 / Virus Database: 267.9.2/55 - Release Date: 7/21/2005
> >
> >
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