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How to shrink LVM group
Posted: 2018/05/21 21:17:46
by Alexegin
Hello all.
I have the following configuration of LVM:
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[root@centos ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
lv_home vg_centos -wi-ao---- 100.00g
lv_root vg_centos -wi-ao---- 50.00g
lv_swap vg_centos -wi-ao---- 7.75g
So, the total size occupied by logical volumes is 157GB.
But, the size occupied by physical volume is:
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[root@centos ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda5 vg_centos lvm2 a--u 502.83g 345.08g
So, the question is - how to remove 345,08GB from physical volume and from volume group - I want to use it in another way, install CentOS 7 for example.
How to shrink partition?
Take a look at the screenshot attached.
Thank you very much for answering in advance.
Re: How to shrink LVM group
Posted: 2018/05/22 11:45:40
by jlehtone
Alexegin wrote:I want to use it in another way, install CentOS 7 for example.
For CentOS 7 I would simply create a new LV for its root, and mount the home and swap just like in CentOS 6.
The tricky part though is the /boot. Would it have enough space for all kernels?
That said there is
pvresize. It can shrink the PV. The size of VG is dictated by the sizes of its PVs.
Once PV has gotten smaller, one can modify the partition table. (I would 1. shrink PV more than necessary, 2. change partition, and 3. expand PV to whole partition.)
/dev/sda5. Is that a logical drive in extended partition of MBR table, or simply fifth partition on GPT?
Re: How to shrink LVM group
Posted: 2018/05/22 15:49:43
by TrevorH
You cannot really coexist CentOS 6 and 7 on the same boot disk. CentOS 7 uses grub2 and that will overwrite CentOS 6's grub legacy boot records and render it unbootable. The only way to do this is to install a second disk and set it to be the boot disk in the BIOS, do your install to that and let it write grub2 to the MBR on there.
On grub legacy it used to be possible to tell it to install into the partition boot record so you could chain that grub off an existing one. With grub2 and the CentOS installer I am not aware that such a thing is still possible.
Re: How to shrink LVM group
Posted: 2018/05/22 19:04:09
by jlehtone
I do agree, but it is not impossible.
On one case I did move the (CentOS 6) contents of /boot from separate partition into the root LV of CentOS 6. Then I did let CentOS 7 repopulate the original /boot. Finally, I did add custom grub2 entry for the CentOS 6 kernel. (Grub2 can mount LVM volumes and load kernel from there.) The major disadvantage is that kernel updates to CentOS 6 will no longer update grub entries (because they cannot see them). This was MBR.
GPT (with uefi boot) is a different story. (I had CentOS 6 functional with EFI.) More possibilities, unless you have allocated all of the disk for one big partition.
Re: How to shrink LVM group
Posted: 2018/05/22 19:51:06
by Alexegin
jlehtone wrote:
/dev/sda5. Is that a logical drive in extended partition of MBR table, or simply fifth partition on GPT?
I have the following partition configuration (see comments after #):
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[root@centos ~]# parted /dev/sda unit MB print
Model: ATA Hitachi HTS72757 (scsi)
Disk /dev/sda: 750156MB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos
Number Start End Size Type File system Flags
1 1.05MB 106MB 105MB primary ntfs boot # /dev/sda1 - MS Windows 7 MBR
2 106MB 209716MB 209610MB primary ntfs # /dev-sda2 - MS Windows 7 disk C:
3 209716MB 210241MB 524MB primary ext4 # /dev/sda3 - mounted at /boot
4 210241MB 750156MB 539916MB extended # /dev/sda4 - container for logical partitions
5 210242MB 750155MB 539914MB logical lvm # /dev/sda5 - LVM
See also the attached screenshot below: