Why Do I Receive Data From A Read Only Share?

[Hardy]

So I have set up a sync to a couple of peers as read only - when it syncs I have noticed that I am receiving some data as well as sending. It's only a small amount (less than 100B/s) while obviously I'm sending more.

 

Anyone know why this is?

[GreatMarko]

When you say you're "receiving some data" - do you mean actual files?! ...or do you mean that your R/O node is just communicating with other nodes? If its the latter, this is normal - nodes regardless of their type still need to "communicate" with each other to determine the states of files and what needs transferring.

[Hardy]

I'm pretty sure is the latter - good to know it's normal  Thanks

[piotrnik]

It's normal for read-only peers to send data both for sync status (eg checksums and other transfer-related info) as well as sending parts of the actual files to other peers that are missing them.  Because they are read-only, they won't sync any files that are changed on their side, but they will sync any unchanged files transferred from the read-write peers.  

 

As an example, assume there is one r/w peer (A) and two r/o peers (B and C). A will send files and changes to B and C.  B and C will share any files (unchanged on their side) between themselves (if A sends it to B, B can forward it to C instead of C having to get it from A). If a new r/w or r/o peer is added (peer D), it can get the files from any combination of A, B, or C.  

By the nature of the torrent system, any peer can get any file pieces from any other peer that possesses them.  Sync adds r/w and r/o levels, but doesn't change this default nature of torrents - the r/w or r/o only affects who can make changes that propagate out through the system, not how the changes transfer between peers.