Resizing OS disks vs Data Disks on an Azure VM
Rucha Shukla
Managed Services Engineer Results driven, customer focused and comfortable working in a fast paced environment
OS Disk:
Purpose: This disk contains the operating system and is used to boot the virtual machine (VM). It’s similar to the C: drive on a physical computer.
Usage: It stores the OS files and system-related data. Typically, you should avoid storing application data or user files on this disk to keep the system running smoothly (not recommended for storing logs).
Management: The OS disk is usually created and attached when the VM is provisioned. Its size can be increased, but this often requires stopping the VM.
The new size should be greater than the existing disk size. The maximum allowed is 4,095 GB for OS disks. (It's possible to expand the VHD blob beyond that size, but the OS works only with the first 4,095 GB of space.)
NEED TO STOP THE MACHINE BEFORE RESIZING. ALWAYS MAKE SURE YOU HAVE A RECENT BACKUP.
After stopping, go here and resize, then turn the machine back on.
Also for this one need to make sure the C drive on the VM itself is extended.
To do this, after you resize the OS disk, restart the VM and go into it.
Go to Computer Management > Storage > Disk Management.
Right click on the C: drive and hit "Extend Volume".
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Typically should not be greyed out and should be able to do "Extend all".
Data Disk:
Purpose: These disks are used to store application data, user files, and other non-system data. They are like additional drives (e.g., D:, E:) on a physical computer.
Usage: Data disks can be added or removed as needed without affecting the OS. They provide flexible storage options for different types of data.
Management: Data disks can be resized without stopping the VM, making them more flexible for dynamic storage needs.
Expanding without downtime is only supported for data disks.
The host cache setting of your disk doesn't change whether or not you can expand a data disk without deallocating your VM.
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