zfs send takes a long time before data is sent

[byteharmony]

I can't say this is critical, but given the magic the team has put out lately I could see someone making this improvement.

When I do a zfs send I usually send the data into pipe viewer (pv) which shows how much data is flowing through the pipe. In some cases with pools with large numbers of volumes and snapshots the data takes time before it starts flowing. Sometimes over a minute.

BK

[byteharmony]

Sometimes the smaller the data amount the longer it seems to take?? last volume i did had only 4.27 KB of data, but it took 5 min 22 seconds before data was sent into the pipe. It instantly completed the send.

BK

[behlendorf]

I've flagged this as a performance issue, perhaps someone can look in to it time permitting.

[byteharmony]

Thanks, here are a few more details for the helpful sole who helps us:
as the number of snapshots for a zvol drops the time to start the send data flowing drops (significantly).

BK

[pdf]

Possibly related to #2131

[behlendorf]

Closing as stale. Several zfs send/recv performance improvements have been made to master.