Hi, I am testing a mirror target for dmsetup. After creating the dm device I cannot the underlying block device. [root@bladelinux01 ~]# dumpe2fs /dev/loop0 | head dumpe2fs 1.41.12 (17-May-2010) Filesystem volume name: <none> Last mounted on: <not available> Filesystem UUID: 9c0f4d5c-55d9-4332-b0e7-f48a19333174 Filesystem magic number: 0xEF53 Filesystem revision #: 1 (dynamic) Filesystem features: has_journal ext_attr resize_inode dir_index filetype sparse_super Filesystem flags: signed_directory_hash Default mount options: (none) Filesystem state: clean Errors behavior: Continue [root@bladelinux01 ~]# dumpe2fs /dev/loop1 | head dumpe2fs 1.41.12 (17-May-2010) Filesystem volume name: <none> Last mounted on: <not available> Filesystem UUID: c16fcae4-2271-4701-a91e-6694962935d0 Filesystem magic number: 0xEF53 Filesystem revision #: 1 (dynamic) Filesystem features: has_journal ext_attr resize_inode dir_index filetype sparse_super Filesystem flags: signed_directory_hash Default mount options: (none) Filesystem state: clean Errors behavior: Continue [root@bladelinux01 ~]# mount /dev/loop0 /mnt/ ; mount | grep loop0 /dev/loop0 on /mnt type ext3 (rw) [root@bladelinux01 ~]# umount /mnt/ [root@bladelinux01 ~]# mount /dev/loop1 /mnt/ ; mount | grep loop1 /dev/loop1 on /mnt type ext3 (rw) [root@bladelinux01 ~]# umount /mnt/ [root@bladelinux01 ~]# dmsetup create raid1 --table "0 204800 mirror core 1 128 2 7:0 0 7:1 0" [root@bladelinux01 ~]# dmsetup table raid1 0 204800 mirror core 1 128 2 7:0 0 7:1 0 [root@bladelinux01 ~]# dmsetup info raid1 Name: raid1 State: ACTIVE Read Ahead: 256 Tables present: LIVE Open count: 0 Event number: 1 Major, minor: 253, 6 Number of targets: 1 [root@bladelinux01 ~]# dmsetup info -c raid1 Name Maj Min Stat Open Targ Event UUID x 253 6 L--w 0 1 1 [root@bladelinux01 ~]# dmsetup deps raid1 2 dependencies : (7, 1) (7, 0) [root@bladelinux01 ~]# dmsetup status /dev/mapper/raid1 0 204800 mirror 2 7:0 7:1 1600/1600 1 AA 1 core I have mounted the newly created dm device and copied some data to it. [root@bladelinux01 ~]# mount /dev/mapper/raid1 /mnt/ ; mount | grep raid1 /dev/mapper/raid1 on /mnt type ext3 (rw) [root@bladelinux01 ~]# cp /var/log/messages /mnt/ [root@bladelinux01 ~]# ls -l /mnt/ total 51 drwx------. 2 root root 12288 Nov 2 22:32 lost+found -rw-------. 1 root root 37417 Nov 2 22:38 messages I have now unmounted the dm device to test if the daya is written to the underlying block device. [root@bladelinux01 ~]# umount /mnt/ [root@bladelinux01 ~]# dmsetup info raid1 Name: raid1 State: ACTIVE Read Ahead: 256 Tables present: LIVE Open count: 0 Event number: 1 Major, minor: 253, 6 Number of targets: 1 Here the open count is "ZERO", but still I cannot mount the underlying block device. [root@bladelinux01 ~]# mount /dev/loop0 /mnt/ mount: /dev/loop0 already mounted or /mnt/ busy [root@bladelinux01 ~]# mount /dev/loop1 /mnt/ mount: /dev/loop1 already mounted or /mnt/ busy But if I remove the dm device created and try to mount the underlying block-device, I can mount both the device which took part in mirroring and I can access the data in both the disk. [root@bladelinux01 ~]# dmsetup remove raid1 [root@bladelinux01 ~]# mount /dev/loop0 /mnt/ [root@bladelinux01 ~]# ls -l /mnt/ total 51 drwx------. 2 root root 12288 Nov 2 22:32 lost+found -rw-------. 1 root root 37417 Nov 2 22:38 messages [root@bladelinux01 ~]# umount /mnt/ [root@bladelinux01 ~]# mount /dev/loop1 /mnt/ [root@bladelinux01 ~]# ls -l /mnt/ total 51 drwx------. 2 root root 12288 Nov 2 22:32 lost+found -rw-------. 1 root root 37417 Nov 2 22:38 messages Why is this behavior. any explanation, please.... -- sanjana