First snapshot of a disk is of size O B

[Sourav97]

Hello,

Today I had taken an instant snapshot of the boot disk of a server and it is the first snapshot , but the size of the snapshot is 0 B.

It would have been genuine if there would been incremental snapshots. But in this case , there are no incremental snapshots here.

Can anyone please help me with this query?

[FrancoGP · Accepted solution]

Hi @Sourav97 ,

Welcome to Google Cloud Community!

Take this with a grain of salt, but I firmly belive this is the answer to you query.
While you are right, snapshots are incremental with the first one being full, instant snapshots and standard snapshots as they have different use cases, they have different mechanisms as well, to ensure the speed of taking the snap and restore, all data is not copied to the snapshot itself as a regular one, it just copies the metadata of your disk and data to know how and where to restore it, and this values are not contemplated in you snapshot size, this is an in-place solution so again, all data won't be copied the same way as in a standard snap, just the pointers (for the first snap)
Any forward modification of files and configurations should be contemplated on your snap.

[Sourav97]

Thanks @FrancoGP  for the response. Appreciate it.

[Sourav97]

One more question, I had created a Win 2k19 VM in GCP with a boot disk of size 50 GB. I had taken a standard snapshot of the boot disk , but the snapshot size appears to be much lesser than the boot disk size. Is there some sort of compression running behind? If so what is the compression factor - is it fixed or its value depends upon some criteria?

Attaching the screenshot

[FrancoGP]

Yes, you are correct.

There is an automated compression mechanism for each snapshot taken. There isn't a lot of documentation regarding which algorithm is used, to say none.
But I can confirm you it's not a fixed %, I went into my environment and checked the ratio between linux and windows, large volumes vs small ones, and all of them varies to a certain degree but not alarming stats, with an overall better result over larger data volumes, which make sense