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FAQ-how to handle the dm-0 device appeared after executing fdisk-1 command

Publication Date:  2012-10-17 Views:  52 Downloads:  0
Issue Description
An ATAE board is connected to a S3200 storage at field, the operating system of board is SLES 10 SP 1. Manage storage with LVM, after LV is made by field engineer, when check hard disks with fdisk command, devices labeled by dm-0 and dm-1 appear.
db1:~ # fdisk -l
Disk /dev/sda: 146.8 GB, 146815733760 bytes
255 heads, 63 sectors/track, 17849 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1         128     1028128+  82  Linux swap / Solaris
/dev/sda2   *         129       17849   142343932+  83  Linux
Disk /dev/sdb: 292.5 GB, 292556898304 bytes
64 heads, 32 sectors/track, 279004 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1       20480    20971504   8e  Linux LVM
/dev/sdb2           20481      279004   264728576   8e  Linux LVM
Disk /dev/sdc: 23.5 GB, 23579049984 bytes
97 heads, 62 sectors/track, 7657 cylinders
Units = cylinders of 6014 * 512 = 3079168 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1        1021     3070116   8e  Linux LVM
Disk /dev/sdd: 32.2 GB, 32212254720 bytes
64 heads, 32 sectors/track, 30720 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1               1       30720    31457264   8e  Linux LVM
Disk /dev/dm-0: 295.6 GB, 295664877568 bytes
255 heads, 63 sectors/track, 35945 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk /dev/dm-0 doesn't contain a valid partition table
Disk /dev/dm-1: 16.1 GB, 16106127360 bytes
255 heads, 63 sectors/track, 1958 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk /dev/dm-1 doesn't contain a valid partition table

Alarm Information
None
Handling Process
Ignore these devices.
Root Cause
1. For new installed SLES 10 SP1 board, check with fdisk command, there is no dm-0 device;
2. Scan all mirrored LUN, check with fdisk command, there is no dm-0 device;
3. Manage storage with LVM. After PV and VG are created, check with fdisk command, there is no dm-0 device. After LV is created and check with fdisk command, there is dm-0 device appeared;
4. According confirmation of SLES engineer, these dm-0 devices are mirror information of LV. When check disk device with fdisk, they are displayed as flash devices. During actual using, we can ignore these devices.

Suggestions
None

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