Re: swidth with mdadm and RAID6

Shailendra Tripathi
2006-09-18T23:24:41Z

Hi Steve,
Your guess appears to be correct. md_ioctl returns nr which
is total number of disk in the array including the spare disks. However,
XFS function md_get_vol_stripe does not take spare disk into account. It
needs to subtract spare_disks as well.
However, md.spare_disks returned by the call returns spare + parity
(both). So, one way could be substract spare_disks directly. Otherwise,
the xfs should rely on md.raid_disks. This does not include spare_disks
and nr.disks should be changed for that.

When I run my program md_info on raid5 array with 5 devices and 2
spares, I get
[root@ga09 root]# ./a.out /dev/md11
Level 5, disks=7 spare_disks=3 raid_disks=5

Steve can you please compile the pasted program and run on your system
with md prepared. It takes /dev/md<no> as input.
In your case, you should get above line as:
Level 6, disks=11 spare disks=3 raid_disks=10

nr=working=active=failed=spare=0;
ITERATE_RDEV(mddev,rdev,tmp) {
nr++;
if (rdev->faulty)
failed++;
else {
working++;
if (rdev->in_sync)
active++;
else
spare++;
}
}

info.level = mddev->level;
info.size = mddev->size;
info.nr_disks = nr;
....
info.active_disks = active;
info.working_disks = working;
info.failed_disks = failed;
info.spare_disks = spare;

-shailendra
The program is pasted below:
md_info.c. Takes /dev/md<no> as name. For example, /dev/md11.

#include<stdio.h>
#include<fcntl.h>
#include<sys/ioctl.h>
#ifndef MD_MAJOR
#define MD_MAJOR 9
#endif

#define GET_ARRAY_INFO _IOR (MD_MAJOR, 0x11, struct md_array_info)

struct md_array_info {
__uint32_t major_version;
__uint32_t minor_version;
__uint32_t patch_version;
__uint32_t ctime;
__uint32_t level;
__uint32_t size;
__uint32_t nr_disks;
__uint32_t raid_disks;
__uint32_t md_minor;
__uint32_t not_persistent;
/*
* Generic state information
*/
__uint32_t utime; /* 0 Superblock update time */
__uint32_t state; /* 1 State bits (clean, ...) */
__uint32_t active_disks; /* 2 Number of currently active disks */
__uint32_t working_disks; /* 3 Number of working disks */
__uint32_t failed_disks; /* 4 Number of failed disks */
__uint32_t spare_disks; /* 5 Number of spare disks */
/*
* Personality information
*/
__uint32_t layout; /* 0 the array's physical layout */
__uint32_t chunk_size; /* 1 chunk size in bytes */

};

int main(int argc, char *argv[])
{
struct md_array_info md;
int fd;

/* Open device */
fd = open(argv[1], O_RDONLY);
if (fd == -1) {
printf("Could not open %s\n", argv[1]);
exit(1);
}
if (ioctl(fd, GET_ARRAY_INFO, &md)) {
printf("Error getting MD array info from %s\n", argv[1]);
exit(1);
}
close(fd);
printf("Level %d, disks=%d spare_disks=%d raid_disks=%d\n",
md.level, md.nr_disks,
md.spare_disks, md.raid_disks);
return 0;
}