Extending A CentOS Disk Without Reboot

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Hello,

Today a virtual server under my administration ran out of disk space, so I had to get extra space to it.. while it was running, because it’s an important web server without any kind of HA/Load Balancing (don’t do that, kids).

So what happened, is that after another administrator had extended the disk from VMWare, I tried to extend it from the OS side.

Everything went well, listing my steps here:

* echo 1 > /sys/class/scsi_device/2\:0\:0\:0/device/rescan
* fdisk /dev/sdb (the usual, delete partition and make a new, bigger one)

Now’s when the problems happened. After writing the partition table I
got the usual “Busy” error. But I needed to do this without downtime. So, what did I try to get the kernel acknowledge the partition size change:

* hdparm -z /dev/sdb
* partx -a -v /dev/sdb
* partprobe -s
* echo “1” > /sys/block/sdb/device/rescan

And while dmesg reported that it recognized the partition change, LVM
did still not see it. So eventually, I was still forced to reboot, after which everything (pvresize, lvresize, resize2fs) worked fine. Environment:

* A VMWare virtual machine
* CentOS 6.7 (Final)

Is there any other way I’m missing? Is this caused by the fact that I
was trying to resize a partition that is under the root file system? If so, then is it really impossible to do it live?

Thanks,

5 thoughts on - Extending A CentOS Disk Without Reboot

  • As far as I know (and perhaps my knowledge is dated) it is not possible to resize a partition on the boot device without a reboot. I’m not sure exactly what you mean by “partition under the root filesystem”, but I’m guessing you mean that you may have been trying to resize /. If that’s the case, then you may be able to do this only if /boot is on a different device.

    If you were resizing / because it filled, what exactly filled up? If it was someplace like /tmp or /var, you may want to consider migrating those to separate filesystems, probably under LVM, so that you have a better chance of this succeeding. If you can have your VMWare admin attach a second device where you can put these filesysems even better, that’s sure to work without requiring a reboot.

    –keith

  • …
    …

    Well, partprobe is the standard advice for this situation, but I don’t think it actively does anything with the -s flag. That could have been the problem, but I’m not certain.

    You didn’t include “pvresize” in that list, so I presume you didn’t do it. That’s the command that will inform LVM of the change.

  • I did not do pvresize because neither “pvs” or “pvdisplay” reported to have free space.

    After reboot they did, after which doing pvresize worked successfully.

    Sander Kuusemets University of Tartu, High Performance Computing, IT Specialist Skype: sander.kuusemets1
    +372 737 5694

  • The curious thing is that a couple of weeks ago, I used parted to resize a GPT partition under Fedora 23, then resized the LUKS device, then the PV. I didn’t have to reboot. I don’t seem to be able to do the same thing under CentOS 7, though that test system didn’t use a LUKS
    encrypted partition.

    I don’t know why this is possible in some circumstances and not others.
    Anyone else?