Date: Tue, 19 Sep 2006 13:13:02 -0400 (EDT)
From: Steve Cousins <cousins@limpet.umeoce.maine.edu>
Reply-To: cousins@umit.maine.edu
To: Shailendra Tripathi <stripathi@agami.com>
cc: xfs@oss.sgi.com
Subject: Re: swidth with mdadm and RAID6
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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;
> > }
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> 
>