Ephemeral type of disk is part of the local virtual machine and it’s not saved any Azure storage. Having said that it’s super faster than other disk types currently. Stateless workloads like Windows Virtual Desktops work well and cost benefits by using such OS Disk type. If you need low read/to write latency to the OS layer and faster OS reimage consider Ephemeral Disk types. The following blog will explain your key matrix, insights of this type of OS Disk, and use case with Windows Virtual Desktop environment.
Azure Disk comparison
| Detail | Ultra Disk | Premium Disk | Standard Disk | Standard HDD |
| Disk Type | SSD | SSD | SSD | HDD |
| Scenario | IO intensive work load | Production and Performance worktype servers used | Web servers, dev/test vm types | Backup, non critical VM types used |
| Max disk size | 65,536 GiB | 32,767 GiB | 32,767 GiB | 32,767 GiB |
| Max throughput | 2,000 MB/s | 900 MB/s | 750 MB/s | 500 MBs |
| Max IOPS | 160,000 | 20,000 | 6,000 | 2,000 |
Ephemeral cost-benefit visibility
Following example shows monthly cost that we can save by using this type of disk
What are ephemeral OS Disk
This type of Disk are local to the VM. Which mean its faster and boot up faster
Also something to remember
- Free to use
- Part of the VM SSD cache
- Image needs to suites to cache
- Work with all type of images
- Lower latency, like local disk
Advantages and disadvantages by using ephemeral Disk
| Keep an eye on | Take advantage of |
| No available for all VM type | Local to VM, no mounting needed, faster provisioning, faster start/stop |
| Cannot be stop – deallocated virtual machine | Popular VM’s for WVD are supported DSv1, DSv2, DSv3, Esv3, Fs, FsV2, GS, M |
| Dependent on cache size | Cost savings. The are FREE |
| Not supported 1. Capturing VM Images 2. Disk snapshots 3. Azure Disk Encryptions 4. Azure Backups 5. Azure site Recovery 6. OS Disk Swap |
Features comparisons Persistent OS Disk vs Ephemeral OS Disk
| Persistent Disk | Feature | Ephemeral Disk |
| All regions | Region Supported | All regions |
| Yes | Disk Snapshots | No |
| Yes | OS Disk Encryption | No |
| OS disk data is preserved | Resizing to a New VM | OS disk data will deleted |
| During the creation & stopped / deallocation | OS Disk resize | During the creation only |
| Yes | STOP VM | No |
| OS disk data written to Azure storage | Data Persistence | OS data written to local VM storage |
| Managed and unmanaged disk | Disk type supported | Managed disk |
| All | VM sizes supported | DSv1, DSv2, DSv3, Esv3, Fs, FsV2, GS, M |
| 2 TiB | Size limit for OS Disk | Cache size of VM or 2 TiB |
