multi: add minimum disk space check

go.mod

@@ -66,6 +66,7 @@ require (
 	go.uber.org/zap v1.14.1 // indirect
 	golang.org/x/crypto v0.0.0-20200709230013-948cd5f35899
 	golang.org/x/net v0.0.0-20191002035440-2ec189313ef0
+	golang.org/x/sys v0.0.0-20200202164722-d101bd2416d5
 	golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2
 	google.golang.org/grpc v1.24.0
 	gopkg.in/errgo.v1 v1.0.1 // indirect