Merge pull request #3931 from kjetilho/feature/optional_scanner

add --no-scan to backup command

changelog/unreleased/pull-3931

@@ -0,0 +1,8 @@
+Enhancement: Allow backup file tree scanner to be disabled
+
+Restic walks the file tree in a separate scanner process to find the total size
+and file/directory count, and uses that to provide an ETA.  This can slow down
+backups, especially of network filesystems.  The new flag `--no-scan`
+can be used to speed up such backups.
+
+https://github.com/restic/restic/pull/3931

cmd/restic/cmd_backup.go

@@ -99,6 +99,7 @@ type BackupOptions struct {
 	UseFsSnapshot     bool
 	DryRun            bool
 	ReadConcurrency   uint
+	NoScan            bool
 }
 
 var backupOptions BackupOptions
@@ -138,6 +139,7 @@ func init() {
 	f.BoolVar(&backupOptions.IgnoreInode, "ignore-inode", false, "ignore inode number changes when checking for modified files")
 	f.BoolVar(&backupOptions.IgnoreCtime, "ignore-ctime", false, "ignore ctime changes when checking for modified files")
 	f.BoolVarP(&backupOptions.DryRun, "dry-run", "n", false, "do not upload or write any data, just show what would be done")
+	f.BoolVar(&backupOptions.NoScan, "no-scan", false, "do not run scanner to estimate size of backup")
 	if runtime.GOOS == "windows" {
 		f.BoolVar(&backupOptions.UseFsSnapshot, "use-fs-snapshot", false, "use filesystem snapshot where possible (currently only Windows VSS)")
 	}
@@ -586,6 +588,7 @@ func runBackup(ctx context.Context, opts BackupOptions, gopts GlobalOptions, ter
 		targets = []string{filename}
 	}
 
+	if !opts.NoScan {
 		sc := archiver.NewScanner(targetFS)
 		sc.SelectByName = selectByNameFilter
 		sc.Select = selectFilter
@@ -596,6 +599,7 @@ func runBackup(ctx context.Context, opts BackupOptions, gopts GlobalOptions, ter
 			progressPrinter.V("start scan on %v", targets)
 		}
 		wg.Go(func() error { return sc.Scan(cancelCtx, targets) })
+	}
 
 	arch := archiver.New(repo, targetFS, archiver.Options{ReadConcurrency: backupOptions.ReadConcurrency})
 	arch.SelectByName = selectByNameFilter

doc/040_backup.rst

@@ -204,8 +204,17 @@ Combined with ``--verbose``, you can see a list of changes:
     modified  /archive.tar.gz, saved in 0.140s (25.542 MiB added)
     Would be added to the repository: 25.551 MiB
 
-.. _backup-excluding-files:
+Disabling Backup Progress Estimation
+************************************
 
+When you start a backup, restic will concurrently count the number of
+files and their total size, which is used to estimate how long it will
+take.  This will cause some extra I/O, which can slow down backup of
+network file systems or fuse mounts.
+
+-  ``--no-scan``  Do not run scanner to estimate size of backup
+
+.. _backup-excluding-files:
 Excluding Files
 ***************