PBS4: How does PBS4 use its cache when a datastore is configured on a S3 bucket?

[guerro]

Hello to everyone,
We're in the process of testing the new beta of Proxmox Backup Server, especially the S3 implementation.
To this moment everything seems to work flawlessly with our Garage S3 compatible cluster, but my main doubt arise about the local cache.
If I restore a backup from the S3 datastore, it looks like both the disk and S3 are being utilized at the same time.
How much of the data is restored from the local cache? Is the cache only used for "indexing" purpose and is not used at all for the data?
Thank you in advance.

 

[Chris]

Hi,
on restore, the chunk is first looked up in the local datastore cache, the client gets it from there if present. On cache miss, the chunk is however fetched from the S3 backend, inserted into the local datastore cache since recently used and then downloaded by the client. That is most likely what you see.