Backups: What does sparse% and x/x MB/s mean?

[Lonnie]

While backing up a Proxmox virtual machine you see these progress indicators:

INFO: status: 36% (193834713088/536870912000), sparse 25% (137619529728), duration 1063, 422/20 MB/s

Status is the overall completion of the backup. Understood.

What does sparse mean? Does this have to do with how much compression is being achieved at this particular moment of the backup? This number increases during the backup progress, but what does it mean exactly? The documentation says that it is the "% of sparse regions". But I'm not sure what that really means.

Also, the 422/20 MB/s, what is the saying? What do the upper and lower values represent? It would seem like the rate would only be one average number at any time during the backup-progress, but instead this always shows 2 different numbers. From reading the documentation, from how I understand it, the first number is the read speed and the second number is the write speed. Is that correct?

 

[dietmar]

What does sparse mean? Does this have to do with how much compression is being achieved at this particular moment of the backup? This number increases during the backup progress, but what does it mean exactly? The documentation says that it is the "% of sparse regions". But I'm not sure what that really means.

Spare is the amount of data containing 'zero' inside the file.

Also, the 422/20 MB/s, what is the saying? What do the upper and lower values represent? It would seem like the rate would only be one average number at any time during the backup-progress, but instead this always shows 2 different numbers. From reading the documentation, from how I understand it, the first number is the read speed and the second number is the write speed. Is that correct?

Yes. They can differ because there is no need to write spare data (zeroes). This is a special form of compression.