I had problems reshaping my RAID6 down 1 disk today and found a
problem in Grow.c:
diff -udpr mdadm-3.1.2/Grow.c mdadm-3.1.2-critical-section/Grow.c
--- mdadm-3.1.2/Grow.c 2010-03-09 23:31:39.000000000 -0500
+++ mdadm-3.1.2-critical-section/Grow.c 2010-06-13 14:57:44.000000000 -0400
@@ -497,7 +497,7 @@ int Grow_reshape(char *devname, int fd,
int rv = 0;
struct supertype *st;
- int nchunk, ochunk;
+ unsigned long nchunk, ochunk;
int nlayout, olayout;
int ndisks, odisks;
int ndata, odata;
After changing this I was able to re-shape the array, it seems it was
overflowing and I had a message saying:
root@billsshack:~/mdadm-3.1.2/ > ./mdadm --grow /dev/md0
--raid-devices=6 --backup-file=/mnt/data1/md-raid6-grow-backup.bak
mdadm: Need to backup 4503599627350016K of critical section..
mdadm: /dev/md0: Something wrong - reshape aborted
Now it works:
root@billsshack:~/mdadm-3.1.2/ > ./mdadm --grow /dev/md0
--raid-devices=6 --backup-file=/mnt/data1/md-raid6-grow-backup.bak
mdadm: Need to backup 20480K of critical section..
root@billsshack:~/mdadm-3.1.2/ > cat /proc/mdstat
Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
[faulty] [linear]
md0 : active raid6 dm-6[0] dm-8[5] dm-5[4] dm-3[3] dm-4[2] dm-7[1]
7814041600 blocks super 0.91 level 6, 1024k chunk, algorithm 2
[6/5] [UUUUUU]
[>....................] reshape = 0.0% (33792/1953510400)
finish=1926.0min speed=16896K/sec
Here's a nice output of GDB:
Breakpoint 1, Grow_reshape (devname=0x7fffffffe390 "/dev/md0",
fd=5, quiet=0,
backup_file=0x7fffffffe3b8
"/mnt/data1/md-raid6-grow-backup.bak", size=1953510400, level=65534,
layout_str=0x0, chunksize=0, raid_disks=6) at Grow.c:939
939 blocks = ochunk/512 * nchunk/512 * odata
* ndata / a;
(gdb) p ochunk/512
$9 = 2048
(gdb) p ochunk/512 * nchunk/512
$10 = -4194304
(gdb) p nchunk
$11 = 1048576
(gdb) p ochunk
$12 = 1048576
(gdb) p ochunk/512
$13 = 2048
(gdb) p nchunk/512
$14 = 2048
(gdb) p 2048*2048
$15 = 4194304
(gdb) p 2048*2048*odata
$16 = 20971520
(gdb) p 2048*2048*odata*ndata
$17 = 83886080
(gdb) p 2048*2048*odata*ndata/a
$18 = 40960
(gdb) p ochunk/512 * nchunk/512 * odata * ndata / a
$19 = 9007199254700032
(gdb) p ochunk/512 * nchunk/512
$20 = -4194304
(gdb)
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