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Old 06-02-2010, 01:53 PM   #1
mixxmaster27
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Registered: Jun 2010
Posts: 2

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understadning /dev/dm-02 mapping and fdisk -l or fdisk -l | less


hey guys, I am an Oracle DBA tasked with setting up an Oracle single instance database using +ASM on RHL.


My question:

ASM is Oracle's storage manager -- Kind of like a LVM specific for Oracle to run on raw devices.

I did an fdisk -l on my server and got this:

Disk /dev/sdf: 323.6 GB, 323695411200 bytes
255 heads, 63 sectors/track, 39353 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdf doesn't contain a valid partition table

Disk /dev/dm-0: 105 MB, 105185280 bytes
255 heads, 63 sectors/track, 12 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-0 doesn't contain a valid partition table

Disk /dev/dm-1: 524 MB, 524943360 bytes
255 heads, 63 sectors/track, 63 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System

Disk /dev/dm-2: 323.6 GB, 323695411200 bytes
255 heads, 63 sectors/track, 39353 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Notice how the pseudo dm-2 has 323.6GB available. However, when I execute df -h /dev/dm-2 it says it is only 7.9GB is size. So, of course I am thinking - where are the remaining 315GB?? Thsi is a concern as I wan t Oracle's Automatic Storage Manager to continue to grow up to 323GB.

df -h /dev/dm-2
Filesystem Size Used Avail Use% Mounted on
- 7.9G 260K 7.9G 1% /dev


Again, my question is: How much space in the raw device do I actually have available? 323.6GB or 7.9GB or is this configuration set-up incorrectly to begin with?

Last edited by mixxmaster27; 06-02-2010 at 01:54 PM.
 
Old 06-02-2010, 05:13 PM   #2
DD554
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Registered: May 2010
Location: Rome, Italy
Distribution: fedora, centos, debian.
Posts: 30

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what kind of device is /dev/dm-2? phisical disk,lvm,something created with ASM?... if df -h /dev/dm-2 is saying 7.9 Gb maybe the partition table is corrupted. erase any partitions, fdisk it,check there are no lvm volumes and format the hard drive again...
ASM may have some setting to create lvm, or some support partitions..
I had a trouble like that and it was because of old lvm volumes on the device.fdisk didn't see and didn't erase them.
 
Old 06-03-2010, 12:17 PM   #3
mixxmaster27
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Registered: Jun 2010
Posts: 2

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/dev/dm-2 is a device mapper device and udev. My subsytem is multipath.
 
  


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