Re: Can't reshape raid0 to raid10

From: "Xiao Ni" <redacted>
To: <redacted>
Sent: Tuesday, December 30, 2014 11:13:41 AM
Subject: Can't reshape raid0 to raid10

Hi Neil

   When I try to reshape a raid0 to raid10, it'll fail like this:

[root@dhcp-12-133 mdadm-3.3.2]# lsblk
NAME                    MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda                       8:0    0 111.8G  0 disk
├─sda1                    8:1    0  1000M  0 part /boot
├─sda2                    8:2    0  29.3G  0 part /
├─sda3                    8:3    0   512M  0 part [SWAP]
├─sda4                    8:4    0     1K  0 part
├─sda5                    8:5    0   102M  0 part
└─sda6                    8:6    0  10.1G  0 part
  └─VolGroup00-LogVol00 254:0    0   9.9G  0 lvm
sdb                       8:16   0 111.8G  0 disk
├─sdb1                    8:17   0     2G  0 part
└─sdb2                    8:18   0    10G  0 part
sdc                       8:32   0 186.3G  0 disk
├─sdc1                    8:33   0     2G  0 part
└─sdc2                    8:34   0    10G  0 part
sdd                       8:48   0 111.8G  0 disk
├─sdd1                    8:49   0     2G  0 part
└─sdd2                    8:50   0    10G  0 part
[root@dhcp-12-133 mdadm-3.3.2]# mdadm -CR /dev/md0 -l0 -n3 /dev/sdb1
/dev/sdc1 /dev/sdd1
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
[root@dhcp-12-133 mdadm-3.3.2]# mdadm --grow /dev/md0 -l10 -a /dev/sdb2
/dev/sdc2 /dev/sdd2
mdadm: level of /dev/md0 changed to raid10
mdadm: add new device failed for /dev/sdb2 as 6: No space left on device

   
   But if I reshape the raid0 to raid5, reshape raid5 to raid0, then reshape
   raid0 to raid10 use
the same command it'll succeed.

[root@dhcp-12-133 mdadm-3.3.2]# mdadm -CR /dev/md0 -l0 -n3 /dev/sdb1
/dev/sdc1 /dev/sdd1
[root@dhcp-12-133 mdadm-3.3.2]# mdadm --grow /dev/md0 -l5
[root@dhcp-12-133 mdadm-3.3.2]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [raid0] [raid10]
md0 : active raid5 sdd1[2] sdc1[1] sdb1[0]
      6285312 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
      
unused devices: <none>

[root@dhcp-12-133 mdadm-3.3.2]# mdadm --grow /dev/md0 -l0
[root@dhcp-12-133 mdadm-3.3.2]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [raid0] [raid10]
md0 : active raid0 sdd1[2] sdc1[1] sdb1[0]
      6285312 blocks super 1.2 512k chunks
      
unused devices: <none>
[root@dhcp-12-133 mdadm-3.3.2]# mdadm --grow /dev/md0 -l10 -a /dev/sdb2
/dev/sdc2 /dev/sdd2
mdadm: level of /dev/md0 changed to raid10
mdadm: added /dev/sdb2
mdadm: added /dev/sdc2
mdadm: added /dev/sdd2

    So I guess it's the problem add the disk to raid10 after the reshaping.
    In the function
super_1_validate, it'll set the  mddev->dev_sectors using the superblock read
from disks.
If it's raid0, the le64_to_cpu(sb-size) is 0. So when add disk to raid10
bind_rdev_to_array
return -ENOSPC.

    When create raid0, it doesn't write give the value to s->size. So the
    sb-size is 0.
I modify the code about Create.c. I'm not sure whether it's right to do so.
But it can resolve
the problem.

diff --git a/Create.c b/Create.c
index 330c5b4..f3135c5 100644
--- a/Create.c
+++ b/Create.c

@@ -489,7 +489,7 @@ int Create(struct supertype *st, char *mddev,
                        pr_err("no size and no drives given - aborting
                        create.\n");
                        return 1;
                }
-               if (s->level > 0 || s->level == LEVEL_MULTIPATH
+               if (s->level >= 0 || s->level == LEVEL_MULTIPATH
                    || s->level == LEVEL_FAULTY
                    || st->ss->external ) {
                        /* size is meaningful */