Azure Ephemeral OS Disk

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

DetailUltra DiskPremium DiskStandard DiskStandard HDD
ScenarioIO intensive work loadProduction and Performance worktype servers usedWeb servers, dev/test vm typesBackup, non critical VM types used
Max disk size65,536 GiB32,767 GiB32,767 GiB32,767 GiB
Max throughput2,000 MB/s900 MB/s750 MB/s500 MBs
Max IOPS160,00020,0006,0002,000
Feature comparisons with different disk types

Ephemeral cost-benefit visibility

Following example shows monthly cost that we can save by using this type of disk

Example with Azure cost calculation

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
VM Disk allocation

Advantages and disadvantages by using ephemeral Disk

Keep an eye onTake advantage of
No available for all VM typeLocal to VM, no mounting needed, faster provisioning, faster start/stop
Cannot be stop – deallocated virtual machinePopular VM’s for WVD are supported
DSv1, DSv2, DSv3, Esv3, Fs, FsV2, GS, M
Dependent on cache sizeCost 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  
Pros and Cons

Features comparisons Persistent OS Disk vs Ephemeral OS Disk

Persistent DiskFeatureEphemeral Disk
All regionsRegion SupportedAll regions
YesDisk SnapshotsNo
YesOS Disk EncryptionNo
OS disk data is preservedResizing to a New VMOS disk data will deleted
During the creation & stopped / deallocationOS Disk resizeDuring the creation only
OS disk data written to Azure storageData PersistenceOS data written to local VM storage
Managed and unmanaged diskDisk type supportedManaged disk
AllVM sizes supportedDSv1, DSv2, DSv3, Esv3, Fs, FsV2, GS, M
2 TiBSize limit for OS DiskCache size of VM or 2 TiB
Key Feature comparisons

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