VMs and scale set instances can be stop-deallocated and restarted from the stop-deallocated state OS disk data written to OS disk are stored in Azure Storageĭata written to OS disk is stored on local VM storage and isn't persisted to Azure Storage. VM sizes that support Premium storage such as DSv1, DSv2, DSv3, Esv3, Fs, FsV2, GS, M, Mdsv2, Bs, Dav4, Eav4 For the cache or temp size in GiB, see DS, ES, M, FS, and GS Key differences between persistent and ephemeral OS disks:Ĭache size or temp size for the VM size or 2040 GiB, whichever is smaller. Ephemeral OS disks are free, you incur no storage cost for OS disks.Lower latency, similar to a temporary disk.Ability to fast reset or reimage VMs and scale set instances to the original boot state.Supported by Marketplace, custom images, and by Azure Compute Gallery (formerly known as Shared Image Gallery).With Ephemeral OS disk, you get lower read/write latency to the OS disk and faster VM reimage. Ephemeral OS disks work well for stateless workloads, where applications are tolerant of individual VM failures but are more affected by VM deployment time or reimaging of individual VM instances. Please share your feedback or questions in the comments section below.Applies to: ✔️ Linux VMs ✔️ Windows VMs ✔️ Flexible scale sets ✔️ Uniform scale setsĮphemeral OS disks are created on the local virtual machine (VM) storage and not saved to the remote Azure Storage. If you are interested to try out GitHub Actions, try out the quick start guide to improve your CI/CD experience today.“Apart from faster reimages, Ephemeral also saves us time setting up machines after each reimage because we no longer need to run “warm-up” scripts, where the sole intention was to forcibly populate more of the disk image on the host” Faster reads as cached parts of the OS disk should persist around after reimage (if it is not dirty).– Jiange Sun, Senior Software Engineer, GitHubĪlong with the re-image being faster than deleting/creating a new VM, GitHub has also seen the below advantages with Ephemeral VMs “The Ephemeral pool ran more customer requests than the non-Ephemeral because of its throughput efficiency. The below chart shows GitHub Actions VM pools jobs reimage performance between Ephemeral and Non-Ephemeral (in seconds). – Chad Kimes, Staff Software Engineer, GitHub “We saw our target machine count reduce by 15-20%.” This also helped in reducing the VM pools size. The average end-to-end time was reduced by 50% after replacing “deleting a VM, recreating it and then run custom extension scripts” with “Ephemeral OS disks Reimage”. The reimage would replace the old OS disk with a new OS disk, and optionally resets the Temp disk contents (if this is included as a parameter) and you would retain, Ephemeral OS disks reimage for VM or reimage for VMSS is equivalent to deleting and re-creating a VM of the same config. It is highly efficient and reliable (99.99%). Reimage can be performed on a single instance VM or VMSS using Ephemeral OS disks. When recreating a VM the corresponding OS caches would be deleted, and that impacted the read IOPS. They needed a reliable and efficient solution to get the VMs faster. For a job that runs no more than 5 mins spending more than 2 mins on setup is an expensive affair. It takes ~2 mins to delete a VM, recreate it, and then run custom extension scripts to get the VM ready for use. These jobs would not take more than 5 mins to complete. GitHub has lots of customers doing very short jobs like updating issues, simple Cron jobs and more. To support this at scale as of January 2022, GitHub Actions would have had to delete and recreate more than 7 million VMs per day. GitHub Actions must always provide a clean VM for each job. Users can build, test, and deploy their code right from GitHub. Whether they want to build a container, deploy a web service, or automate welcoming new users to their open-source projects-there’s an action for that. GitHub Actions makes it easy for customers to automate all their software workflows, with world-class CI/CD. Azure Compute > How GitHub Actions handles CI/CD scale on short-running jobs with Ephemeral OS disk Reimage
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