illumos gate

The first access to a disk block can incur a performance penalty on some platforms (e.g. AWS's EBS, VMware VMDKs). Therefore it is recommended that volumes be "thick provisioned", where supported by the platform (VMware). Thick provisioning is time consuming and often is ignored. If the thick provision step is omitted, customers will see suboptimal performance until we have written to all parts of the LUN. ZFS should be able to initialize any unused storage to remove any first-write penalty that exists.