Selecting Volume Size When Creating Instance From Pre-configured Image

Slightly related to:

Is the 80GB a single disk?

Storage: instance size vs. block storage

When booting from a pre-configured image, (e.g Ubuntu-16.04, 2.20 GB), if I understand things correctly, any size set on the instance is ephemeral but could be saved in a snapshot image which would then count against the 100GB of block storage.

A few follow-up questions:

  1. Need one increase the size of the instance from 2.20GB to 80GB in order to make use of the 80 GB SSD Disk or do I need to attach a separate volume?

  2. Are all volumes block storage that do not make use of the 80GB SSD? Or put a different way, is the only way to use the 80GB SSD by setting the initial instance size?

  3. I’m assuming that the minimum size required to launch the instance is too small in the long run (with installation of other programs), but I trust the operating system also need not have 80GB either. The fact that volumes can be extended notwithstanding, is there optimal initial minimum size for instances?


It’s a bit complicated and I’m not sure I understand fully your questions: it’s very hard to have this sort of conversations in general terms because the topic is complex. It would be much easier if you detailed what exactly you want to do, like what sort of applications are you have in mind, how those are going to use disk space, networks etc… then we can give you more specific suggestions.

Let me try to add some screenshots to explain some basic things. When you start the wizard to create a new instance you’re presented with a lot of options. Let’s assume you want to boot from one of the default images. You can choose to a new instance from an ephemeral volume or not using the Create New Volume button: No means the new instance will live in an ephemeral volume. Ephemeral means that once you destroy the instance, the volume will also be destroyed.

If you choose to create a volume for the new instance then you get to pick the size of such volume. A minimum size is automatically assigned based on the image you select below. For example, a CentOS-6 image will suggest a volume size of at least 11GB. Ubuntu 16.04 will require at minimum 3GB, etc.

That volume size is the bare minimum to boot the OS: if you think you’ll need more disk space for your root and /boot partitions then you need to adjust those sizes.

The 80GB size you see on the Flavor screen is a default amount of storage included in that flavor.

You can probably resize the volume if the instance is paused or suspended but I wouldn’t trust that process. You could attach a separate volume to grow some space but why would you want to do that? so complicated. Much better to destroy and build another instance of the right size. Even if you run WordPress and MySQL on a cloud, you should set things up in a way that you can move the application from one server to another with minimum downtime.

All the storage on DreamCompute is made of the same thing: it’s a large Ceph cluster, all SSD. Is this what you mean?

There is a minimum but the optimal depends on what you need to do with it.

That was very helpful, thanks! You’re definitely getting at my question which in the end has to do with where/when/how the 80GB for the instance and the 100GB of block storage get allocated.

One interpretation of this is that whenever an instance is launched from a Cent08-6 boot volume, it is automatically launched with the equivalent of an 80GB SSD attached to it, 8.00GB of which will already be taken up by the operating system. This would be in addition to the 100GB of block storage included.

If I’m understanding you correctly however, this is not the case. Rather, if you launch an instance from an image or instance snapshot and choose to create a new volume, then the default size of the instance will be the size listed on the source unless you increase it yourself. This supersedes the default size listed on the flavor. If you choose to delete the volume on instance delete, then it is ephemeral and will not count against your 100GB quota.

What happens if you choose to create your instance from a volume or volume snapshot? Since there is no longer an option to change the volume size, does that mean that the server will be launched with the default size of the volume/volume snapshot or the default size of the flavor? If it’s the former, in what situation would the default size of 80GB come into play?

Sooo complicated, right? :slight_smile:

First, one basic thing: with a DreamCompute account you get 100GB block storage allowance included in the basic price. How you use that block storage allowance is up to you. So, for example, if you only run ephemeral instances and no volumes, you never use any of that 100GB quota.

If you create instances from volume, then the block storage quota is used, detracting whatever instance size you picked from the 100GB included (or more, if you bought more).

Sorry, I don’t understand this part. It would be helpful if you could provide screenshots or the command you’d use to create this.

If a volume is ephemeral or not depends on how you created the VM; it has nothing to do whether you choose to delete something.

Volumes are by definition block storage, so any of those is part of the 100GB pool. When you try to create a new instance from a volume, you don’t have the option to create a new volume from it nor you can adjust its disk size. A new VM will be launched with the disk size of that volume.

That 80GB is the size of the root disk of all ephemeral volumes. So if you create a new instance without creating a new volume, you cannot pick the size of the root disk and a default one of 80GB will be assigned to the VM.

Okay, I think I’ve got it now:

Ephemeral volumes are created when you choose to boot from an image or image snapshot and set the “create a new volume” toggle to “No”. In these cases, the size of the instance root disk will automatically be 80GB, but the 80GB’s will not count against your 100GB quota.

If you choose to boot from an image or image snapshot and set the “create a new volume” toggle to “Yes” then, you must specify the size of the root disk. If you do not, the size will default to the size of the chosen image or instance snapshot. Since you have chosen to create a new volume, the size of the volume will count against your 100GB quota.

If you choose to create an instance from a volume or volume snapshot, then the size of the root disk will default to the size already specified on your chosen volume/volume snapshot. This size will count against your 100GB quota.

Thanks for hanging in there with me!

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