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Old 03-17-2010, 04:01 AM   #1
Registered: Apr 2004
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SAN LUN disk space and /dev/dm-5

I got some space from a SAN LUN to a redhat box. If I do "fdisk -l", I can see the disk size under various /dev/* like /dev/hda, /dev/hdd, /dev/dm-4, /dev/dm-5. I made a Linux partition on the /dev/dm-5 which became /dev/dm-5p1 but I cannot see the file /dev/dm-5p1 anywhere in the system. What is the /dev/dm-5p1 and how can I actually see it?

Old 03-17-2010, 11:59 AM   #2
Registered: Jan 2005
Location: Shropshire, England, UK
Distribution: RedHat, Fedora, CentOS..........
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The dm- devices are part of the device mapper system. They are not how I would recommend accessing the disks that you have been allocated.

I would suggest that first you look at the output of the command

This should show you what hardware changes the kernel has seen including detecting the SAN disks and usually what device has been assigned.

I would expect there to be something showing the drive being detected and normally you would get a device such as

assigned to the first disk (note: this may be sdb sdc .... etc depending on the hardware that is local to your server so be careful).

You can also look at

cat /proc/partitions
Which will show the drives and partitions the system can see. You will get an output similar to the list below but which will vary dependant upon your hardware.

# cat /proc/partitions
major minor #blocks name

8 0 976761527 sda
8 1 200781 sda1
8 2 976559220 sda2
8 16 976761527 sdb
8 17 200781 sdb1
8 18 976559220 sdb2
The disks above are split into 2 partitions on each disk (note that the numbers are disk/partition sizes and the 2 disks above are identical in size)

If you can post more information from dmesg and the /proc/partitions file it should be easier to identify what hardware your OS is seeing.


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