Re: Shrinking number of devices on a RAID-10 (near 2) array

[Andy Smith <andy@strugglers.net>]

On Sun, Aug 24, 2014 at 02:39:44PM +0000, Andy Smith wrote:
> $ sudo ./mdadm /dev/md2 --grow --raid-devices=4
> mdadm: Cannot set new_data_offset: RAID10 reshape not
>        supported on this kernel

Grow.c from latest git:

2397                         err = sysfs_set_num(sra, sd, "new_offset",
2398                                             new_data_offset);

For the first device in the for loop (sda3), the above line 2397 is
returning -1.

2399                 }
2400                 if (err < 0) {
2401                         if (errno == E2BIG && data_offset != INVALID_SECTORS) {
2402                                 pr_err("data-offset is too big for %s\n",
2403                                        dn);
2404                                 goto release;
2405                         }
2406                         if (sd == sra->devs &&
2407                             (errno == ENOENT || errno == E2BIG))
2408                                 /* Early kernel, no 'new_offset' file,
2409                                  * or kernel doesn't like us.
2410                                  * For RAID5/6 this is not fatal
2411                                  */
2412                                 return 1;

It reaches here line 2412 with errno == E2BIG.
/sys/block/md2/md/dev-sda3/new_offset exists.

From strace:

open("/sys/block/md2/md/dev-sda3/new_offset", O_WRONLY) = 4
write(4, "128", 3)                      = -1 E2BIG (Argument list too long)
close(4)                                = 0

Not sure where to debug next.

Cheers,
Andy

-- 
> The optimum programming team size is 1.
Has Jurassic Park taught us nothing?
 — pfilandr
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