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Old 05-02-2013, 11:53 AM   #1
UnhandledException
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Questions on the fstab file


Here is the output from my fstab file

> cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Mon Mar 25 03:15:26 2013
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/vg_jimvmserver-lv_root / ext4 defaults 1 1
UUID=2a1919c4-1101-43e4-a7be-2706046ad425 /boot ext4 defaults 1 2
/dev/mapper/vg_jimvmserver-lv_home /home ext4 defaults 1 2
/dev/mapper/vg_jimvmserver-lv_u01 /u01 ext4 defaults 1 2
UUID=f333e8ae-f942-4852-bdfb-263573f448a8 /virt_Machine ext4 defaults 1 2
/dev/mapper/vg_jimvmserver-lv_swap swap swap defaults 0 0
tmpfs /dev/shm tmpfs defaults 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0





Based on the two UUIDs I assume that tells me there are 2 physical hard-drives, correct?
UUID=2a1919c4-1101-43e4-a7be-2706046ad425
UUID=f333e8ae-f942-4852-bdfb-263573f448a8

For the items that you see below, how can you tell on which of the above two hard-drives that the following items are located?
/dev/mapper/vg_jimvmserver-lv_root /
/dev/mapper/vg_jimvmserver-lv_home /home
/dev/mapper/vg_jimvmserver-lv_u01 /u01
/dev/mapper/vg_jimvmserver-lv_swap swap
 
Old 05-02-2013, 11:58 AM   #2
lleb
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Code:
 # pvdisplay -v
that will display what vgroup is on what drive. example:

Code:
[root@centos ~]# pvdisplay -v
    Scanning for physical volume names
  --- Physical volume ---
  PV Name               /dev/sda2
  VG Name               vg_centos
  PV Size               1.82 TiB / not usable 4.00 MiB
  Allocatable           yes (but full)
  PE Size               4.00 MiB
  Total PE              476806
  Free PE               0
  Allocated PE          476806
  PV UUID               DLsmEj-NyRX-4v8T-iuew-R0ol-LWj8-KxB1lf
*edit* to add a link for you:

http://www.datadisk.co.uk/html_docs/redhat/rh_lvm.htm

Last edited by lleb; 05-02-2013 at 11:59 AM.
 
Old 05-02-2013, 12:30 PM   #3
UnhandledException
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Quote:
Originally Posted by lleb View Post
Code:
 # pvdisplay -v
that will display what vgroup is on what drive. example:

Code:
[root@centos ~]# pvdisplay -v
    Scanning for physical volume names
  --- Physical volume ---
  PV Name               /dev/sda2
  VG Name               vg_centos
  PV Size               1.82 TiB / not usable 4.00 MiB
  Allocatable           yes (but full)
  PE Size               4.00 MiB
  Total PE              476806
  Free PE               0
  Allocated PE          476806
  PV UUID               DLsmEj-NyRX-4v8T-iuew-R0ol-LWj8-KxB1lf
*edit* to add a link for you:

http://www.datadisk.co.uk/html_docs/redhat/rh_lvm.htm

Thanks but my main objective is to understand the content of the file and the data I am seeing.

Also, when I do execute the "pvdisplay -v" command it doesn't help explain what I see and it only displays one physical volumne although there are two.

> pvdisplay -v
Scanning for physical volume names
--- Physical volume ---
PV Name /dev/sda2
VG Name vg_jimvmserver
PV Size 465.27 GiB / not usable 3.00 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 119109
Free PE 47429
Allocated PE 71680
PV UUID R57HeX-nKIg-KpZy-2Qhp-Aava-Gz52-g2lol9
 
Old 05-02-2013, 12:42 PM   #4
TobiSGD
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Quote:
Originally Posted by UnhandledException View Post
Based on the two UUIDs I assume that tells me there are 2 physical hard-drives, correct?
No, UUIDs are per partition, not per harddrive. It tells you that two of your partitions, those mounted at /boot and at /virt_Machine, are identified by their UUID to know where to mount them, in opposite to the other partitions in that machine, that are residing on a LVM volumegroup and identified by the device nodes (/dev/mapper/vg_jimvmserver-lv_*).

The output of pvdisplay shows that you have one physical volume /dev/sda2 (one partition on one of your physical drive) that is used to host that volumegroup.
 
Old 05-02-2013, 01:25 PM   #5
UnhandledException
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Quote:
Originally Posted by TobiSGD View Post
No, UUIDs are per partition, not per harddrive. It tells you that two of your partitions, those mounted at /boot and at /virt_Machine, are identified by their UUID to know where to mount them, in opposite to the other partitions in that machine, that are residing on a LVM volumegroup and identified by the device nodes (/dev/mapper/vg_jimvmserver-lv_*).

The output of pvdisplay shows that you have one physical volume /dev/sda2 (one partition on one of your physical drive) that is used to host that volumegroup.
Had to read it a couple of times and able to follow the logic what what I am seeing and what it represents. Thanks.
 
Old 05-02-2013, 03:57 PM   #6
PTrenholme
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Just so you can be a little more confused , a logical volume group (VG) can be made up of several different physical devices, and that VG can contain many different logical volumes. Each LV will have its own UUID and "logical" partition.

What your fstab is telling you is that you have a VG (vg_jimvmserver) containing several different LVs. This is only "logically" related to the actual physical partition (sda2) containing the different LVs.

Note, for future reference, that any errors in a LV must be corrected in the LV as mounted by the device mapper (dm) software, not on the actual physical device. I.e., do not ever run fsck on /dev/sda. (My fingers were once burned.)
 
Old 05-02-2013, 10:04 PM   #7
chrism01
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To check actual (physical) disks,
Code:
# lowercase L switch here ...
fdisk -l

# this is helpful to you also
blkid
 
  


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