Improve resilver ETAs

When resilvering the estimated time remaining is calculated using
the average issue rate over the current pass.  Where the current
pass starts when a scan was started, or restarted, if the pool
was exported/imported.

For dRAID pools in particular this can result in wildly optimistic
estimates since the issue rate will be very high while scanning
when non-degraded regions of the pool are scanned.  Once repair
I/O starts being issued performance drops to a realistic number
but the estimated performance is still significantly skewed.

To address this we redefine a pass such that it starts after a
scanning phase completes so the issue rate is more reflective of
recent performance.  Additionally, the zfs_scan_report_txgs
module option can be set to reset the pass statistics more often.

Reviewed-by: Akash B <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #14410 

1 files changed, 7 insertions, 0 deletions

diff --git a/man/man4/zfs.4 b/man/man4/zfs.4
index e20d60134..6f260660e 100644
--- a/man/man4/zfs.4
+++ b/man/man4/zfs.4
@@ -1890,6 +1890,13 @@ I/O.
 In this case (unless the metadata scan is done) we stop issuing verification I/O
 and start scanning metadata again until we get to the hard limit.
 .
+.It Sy zfs_scan_report_txgs Ns = Ns Sy 0 Ns | Ns 1 Pq uint
+When reporting resilver throughput and estimated completion time use the
+performance observed over roughly the last
+.Sy zfs_scan_report_txgs
+TXGs.
+When set to zero performance is calculated over the time between checkpoints.
+.
 .It Sy zfs_scan_strict_mem_lim Ns = Ns Sy 0 Ns | Ns 1 Pq int
 Enforce tight memory limits on pool scans when a sequential scan is in progress.
 When disabled, the memory limit may be exceeded by fast disks.