Restores and deep verifies requested every blob separately: a new file handle and a seek on
the location each time. They read the blobs of a snapshot in the order they were written, so
the stream of the pack read last now stays open and is read on; a jump backwards, to another
pack, or more than 8 MiB ahead opens the pack again at the offset, as before. On a Hetzner
Storage Box over SMB, restoring 86 MB in 202 files went from 0.78 MB/s to 4.2 MB/s.
