Re: swidth with mdadm and RAID6

Steve Cousins
2006-09-19T17:51:17Z

On Tue, 19 Sep 2006, Steve Cousins wrote:

>
> Hi Shailendra,
>
> I ran the program and it reports:
>
> Level 6, disks=11 spare_disks=1 raid_disks=10
>
> which looks good. I don't understand why you got:

To me this looks correct but I was re-reading your original message and
you said:

> > In your case, you should get above line as:
> > Level 6, disks=11 spare disks=3 raid_disks=10

I don't understand why we should expect parity disks to be included as
spare disks.

Steve

> Level 5, disks=7 spare_disks=3 raid_disks=5
>
> Why would it have 3 spare_disks?
>
> Thanks,
>
> Steve
>
> ______________________________________________________________________
> Steve Cousins, Ocean Modeling Group Email: cousins@umit.maine.edu
> Marine Sciences, 452 Aubert Hall http://rocky.umeoce.maine.edu
> Univ. of Maine, Orono, ME 04469 Phone: (207) 581-4302
>
> On Mon, 18 Sep 2006, Shailendra Tripathi wrote:
>
> > 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;
> > }
> >
> >
> >
> >
> >
> >
> >
>
>