If ufs_WRITES is non-zero, the number of bytes outstanding for writes on a file is checked. See ufs_HW to determine whether the write should be issued or deferred until only ufs_LW bytes are outstanding. The total number of bytes outstanding is tracked on a per-file basis so that if the limit is passed for one file, it won't affect writes to other files.
0 (disabled) or 1 (enabled)
When you want UFS write throttling turned off entirely. If sufficient I/O capacity does not exist, disabling this parameter can result in long service queues for disks.