![]() ![]() All data would have to be kept either on separate disks, on different VMs or on other storage sources and so that the application state is not dependent on the VM. This all sounds good but when would you want to use one of these, when would you have a VM with a non-persistent OS disk?Īny VM that is built from an image either from the Azure marketplace or a custom uploaded image can be used but the workload would have to be stateless. ![]() Note: Data disks will not be ephemeral and therefore kept on remote storage (for most VM sizes at least). As an ephemeral OS disk is free, this means you would only need to price for your data disks (if required). You have to include this in your pricing estimates and this price varies depending on disk type, capacity and Azure region. A point I regularly have to make to customers is that the storage cost of the OS disk is not included in your VM compute costs. It gets better because in addition to this the cost of an ephemeral OS disk is zero. This will provide for lower latency and faster performance. If you choose to use an ephemeral OS disk then your OS disk will be stored on the same host as your VM and it will be kept on SSD storage. they are not stored on the same host as the VM. With most Azure VMs the disks are kept on remote storage, i.e. ![]() This is used as local storage by Azure to improve VM performance. This may sound familiar and yes it operates in exactly the same way as the temp storage (D drive) does. If there is an issue with the VM where you need to either redeploy to another host or perform any action that would deallocate the VM then it will be re-imaged with a new OS disk from the image that was used to create it. Essentially what this means is that the disk is non-persistent so any data written to this disk will be lost should the VM get deallocated. If you look up the word ephemeral in the dictionary you will see it is defined as “something lasting for a very short time”. Ephemeral disks are something that have been in preview for a while now but have only very recently became generally available. ![]()
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