fdisk shows no free sectors available, however a reboot fixes it, why?

JockVSJock · 08-10-2016, 01:03 PM

A partition has run out of space on a RHEL5 VM:

Code:

/dev/mapper/VolGroup01-LogVol00
                       26G   22G   25G  98% /ora

Using blkid, pvs, vgs, lvs and df -ha, I confirm the Physical Volume, Logical Volume and Group Volume and increase the disk size in vCenter.

Using fdisk, I try to create another primary partition (we only can create 3 primary and one logical)

Code:

Disk /dev/sdg: 26.6 GB, 26687091200 bytes


   Device Boot      Start         End      Blocks   Id  System
/dev/sdg1               1        1698    13631487+  8e  Linux LVM
/dev/sdg2            1698        3394    13630817   8e  Linux LVM

However when I go to add /dev/sdg3, I get the following from fdisk

Code:

fdisk no free sectors available

I try to run partprobe, hoping this would pick up space added to the data disk no nothing.

For the hell of it, I reboot and I try fdisk again and I'm able to proceed to add the new partition and using LVM successfully grow the disk.

I don't understand why fdisk wasn't allowing for the creation of the new disk, however a reboot fixed it...?

Emerson · 08-10-2016, 01:52 PM

Probably tmp files got deleted.

JockVSJock · 08-10-2016, 05:51 PM

Quote:

Originally Posted by Emerson

Probably tmp files got deleted.

I'm not sure what tmp files that you are referring to?

syg00 · 08-10-2016, 06:44 PM

Hard disks traditionally didn't get bigger during running. You powered a machine down and swapped out the disk.
More recent versions are more amenable to this. From your own description, partprobe did nothing, so fdisk had nothing new to work with.

jefro · 08-10-2016, 07:14 PM

Some program locked the space?

smallpond · 08-10-2016, 07:15 PM

The kernel keeps a copy of the partition table. After making changes to the disk you need to reread the table by doing the command below. Reboot fixes this as well.

Code:

blockdev --rereadpt /dev/sdg

It is not uncommon to use this in a SAN when a disk has been made larger.

JockVSJock · 08-10-2016, 08:42 PM

Quote:

Originally Posted by smallpond

The kernel keeps a copy of the partition table. After making changes to the disk you need to reread the table by doing the command below. Reboot fixes this as well.

Code:

blockdev --rereadpt /dev/sdg

It is not uncommon to use this in a SAN when a disk has been made larger.

I couldn't even add a partition of 25 GB. I had to reboot first and then I was able to add the partition of 25 GB, ran partprobe and then went thru the LVM steps successfully.

And yes you are correct, this is all SAN storage.

TenTenths · 08-11-2016, 03:04 AM

Quote:

Originally Posted by JockVSJock

Using blkid, pvs, vgs, lvs and df -ha, I confirm the Physical Volume, Logical Volume and Group Volume and increase the disk size in vCenter.

I don't understand why fdisk wasn't allowing for the creation of the new disk, however a reboot fixed it...?

Quote:

Originally Posted by syg00

Hard disks traditionally didn't get bigger during running. You powered a machine down and swapped out the disk.
More recent versions are more amenable to this. From your own description, partprobe did nothing, so fdisk had nothing new to work with.

That ^^^^^

VMs (unless the "guest" OS has been specifically patched / moduled to be aware of their underlying virtualization platform) will only detect changes to the disk size when rebooted, or in the case of Citrix XenServer restarted.