Let’s say you need a Linux Virtual Machine (VM) to do some simple tasks or even host a low to medium traffic web site. You spin up one of the canned Linux images on Azure like CentOS and you find yourself with at least a 32GB disk which has more than 28GB of free space. Is it safe to use this free space for your application or web site(s) without adding a second disk as a data disk?
There are certainly some considerations that must be explored – namely performance and persistence / backup.
Performance
Putting your application and its data on the same disk as the OS is not widely accepted as best practice. But, in many cases, this setup provides more than acceptable performance AND it is considerably easier and lower cost.
Generally the OS is not doing much other than servicing your application and often those processes are running from memory and not being loaded from disk. You should consider doing OS updates and other OS specific maintenance during windows of low load on your application or web site.
So before you add the data disk, do some testing of your application installed on the OS disk – if the performance is acceptable, save yourself the trouble of adding the additional disk. Our testing shows WordPress web sites hosted with CentOS on F1 VMs can easily serve 1000s of pages per hour with response times less than 250ms.
Persistence / Backup
Yes, the OS disk is persistent, it has to be otherwise you couldn’t shutdown or deactivate the VM and later bring it back up. So there are no worries about losing your application or site data because of the persistence issue. But you should have some means to keep a backup of your web sites or applications just for safety’s sake.