Hi guys. I'm currently using iwStack's Cloud VPS Hosting, and I have a problem to discuss.
iwStack use CloudStack for their Cloud VPS Hosting, and in CloudStack, whenever you create a VM instance using their provided OS template images (at least for Centos), two storage volumes are created for each VM: ROOT and DATA. According to their support, ROOT is like C: drive, where it contains the OS files, etc, and DATA is like the D: drive, where people install their apps, store their data, etc. (This is their take, not mine. I always like to install everything on C: on my own Windows PC).
However, if I manually install Centos and use the option to install Centos over the entire drive, then only one volume is created which contains everything: ROOT.
CloudStack also allows you to take Snapshots of these ROOT and DATA volumes, to create their backups. Later on, if you want to restore a volume from its Snapshot, then you have to regenerate a new volume, using the Snapshot. Then detach the old volume from the VM, and attach the newly generated volume in its place.
The problem is, according to iwStack's support, CloudStack does NOT allow you to detach a ROOT volume from a VM ! You can ONLY detach/attach DATA volumes, but not ROOT volumes. This I think is problematic, because say I have a VM with both ROOT and DATA volumes, and some problem came and I restored ONLY the DATA volume, there will be problems on next system boot, because the ROOT volume is still the current state one, while the DATA volume is from a previous state. So won't this cause a consistency issue between the two volumes ?
Anyways, my question is, given this problem, how can I consistently backup/restore volumes, so that there are no inconsistency issues ? Does anyone know ?
Try the snapshot feature on your Cloudstack to backup both the data & root disk. Right now there is no option available on Cloudstack to just restore your VM's root disk (similar to restoring the vm from snapshot) in case of root disk corruption, you need to attach the disk on a new instance and then have to restore/read the data on the new VM. Also you cannot detach a root volume when it is running VM. Hope it helps!
AssistanZ - Beyond Boundaries... Cloudstack Consultancy / 24x7 Web Hosting Support / 24x7 Server Management / Infrastructure Management Services Web & Mobile Apps Development / Web Designing Services / Php, Grails, Java Development