Re: swidth with mdadm and RAID6

[Shailendra Tripathi <stripathi@xxxxxxxxx>]

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;
}