Re: mdadm "hang", 100% CPU usage when trying to create RAID-1 array with external bitmap

[Neil Brown <neilb@suse.de>]

On Wed, 14 Jul 2010 12:53:45 +0200
Tomasz Chmielewski <mangoo@wpkg.org> wrote:

> I'm trying to create RAID-1 with external bitmap with this command:
> 
> mdadm --create /dev/md11 --level=1 --bitmap=/mnt/src/bitmap --raid-devices 2 /dev/storage/origin missing
> 
> 
> /dev/storage/origin is 1.2 TB; is placed on "stacked" block devices like this:
> 
> RAID-5 -> dm-crypt -> LVM-2 -> /dev/storage/origin
> 
> 
> /mnt/src/bitmap is technically the same stacked device, except the last LVM volume:
> 
> RAID-5 -> dm-crypt -> LVM-2 -> /dev/storage/src -> /mnt/src/bitmap
> 
> (although I tried to keep bitmap outside of this RAID-5 device, and it was still hanging).
> 
> 
> When started with "strace", mdadm hangs with 100% CPU usage after opening /mnt/src/bitmap:
> 
> (...)
> rename("/var/run/map.new", "/var/run/map") = 0
> flock(3, LOCK_UN)                       = 0
> close(3)                                = 0
> munmap(0x6ff40000, 4096)                = 0
> unlink("/var/run/map.lock")             = 0
> ioctl(4, 0x800c0910, 0x77f5f89c)        = 0
> fstat64(4, {st_mode=S_IFBLK|0600, st_rdev=makedev(9, 1), ...}) = 0
> fstat64(4, {st_mode=S_IFBLK|0600, st_rdev=makedev(9, 1), ...}) = 0
> ioctl(4, 0x800c0910, 0x77f5f7cc)        = 0
> ioctl(4, 0x40480923, 0x77f5f854)        = 0
> access("/mnt/src/bitmap", F_OK)         = -1 ENOENT (No such file or directory)
> open("/mnt/src/bitmap", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3
> 
> 

Hmm... that's rather embarrassing.
This patch should fit it.  Or you can explicitly set a bitmap chunk size -
aim for several megabyte.

Thanks for the report,
NeilBrown

diff --git a/bitmap.c b/bitmap.c
index beef2dc..44a8677 100644
--- a/bitmap.c
+++ b/bitmap.c
@@ -373,7 +373,7 @@ int CreateBitmap(char *filename, int force, char uuid[16],
 		 */
 		chunksize = DEFAULT_BITMAP_CHUNK;
 		/* <<20 for 2^20 chunks, >>9 to convert bytes to sectors */
-		while (array_size > (chunksize << (20-9)))
+		while (array_size > ((unsigned long long)chunksize << (20-9)))
 			chunksize <<= 1;
 	}
 




> I see no disk activity when this happens.
> 
> 
> # mdadm -V
> mdadm - v3.1.2 - 10th March 2010
> 
> Kernel is 2.6.34.1 (tried also 2.6.28.7), 32 bit x86 system.
> 
> Or, I didn't wait long enough? So far, it takes about an hour to create this array...
> 
> Creating smaller arrays (i.e. 8 GB) in a similar configuration works fine.
> 
>