[CentOS] Extending a CentOS disk without reboot

Mon Dec 21 19:36:17 UTC 2015
James A. Peltier <jpeltier at sfu.ca>

----- Original Message -----
| 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,
| --
| Sander Kuusemets
| University of Tartu, High Performance Computing, IT Specialist

If the disk is not the OS disk I never put a partition table on it if it's going to be used with tools like LVM.  I simply create a full disk physical volume and provision it using volume groups and logical volumes.  In this case I just rescan the bus to see the new size, do a pvscan/presize and then expand the VGs or LVs as necessary.

James A. Peltier
IT Services - Research Computing Group
Simon Fraser University - Burnaby Campus
Phone   : 604-365-6432
Fax     : 778-782-3045
E-Mail  : jpeltier at sfu.ca
Website : http://www.sfu.ca/itservices
Twitter : @sfu_rcg
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