Reinstalling SunOS 4.1.4 without CD drive

On Fri, 2 Oct 2015, Eric Christopherson wrote: SCSI disks are most often shipped formatted with a pool of spare sectors available beyond the nominal externally visible capacity, although the firmware of many allows reformatting with the size of the pool altered, at the most extreme to zero. The pool is often partitioned into concentric zones, called "notches" in SCSI-speak, with a different number of spares assigned per notch (the number of regular data sectors per track will also vary between notches then), although not all firmware exposes notches to interfacing software, and some firmware may not allow reformatting at all. Other than as parameters for the SCSI format command and statistics these spare sectors are invisible to software and are allocated to replace sectors at failed medium spots transparently, although often at a performance cost, because of the out-of-place location of reallocated sectors incurring an additional seek or rotational delay in linear access. Reformatting a drive that has reallocated sectors present will normally reduce the cost or remove it altogether as logical sector positions are reassigned in a linear manner with bad spots already taken into account (skipped over). When reallocation fails because of the pool of spares having exhausted, the originating SCSI command will return a hard failure. The same will happen when a medium error happens and reallocation has been disabled. There are two control bits which control reallocation, ARRE and AWRE, which enable sector reallocation on reads and writes respectively. In the former case reallocation is only made when a medium error is benign enough for error correction (if implemented) to be able to recover data actually read; firmware will usually retry a read a number of times before it gives up and returns a hard error. I have actually seen such retries to succeed sometimes, at which point reallocation prevented further issues at the particular logical sector. In the latter case reallocation is always made for writes to sectors previously observed as bad and not reallocated in a read. Which is why wiping out a disk which previously returned read errors will normally fix it from the logical point of view, without the need to reformat it. When the pool of spare sectors has been exhausted, the only way to revive a failing disk is to reformat it with its externally visible capacity reduced, as long as the firmware permits it. Marking blocks as bad at the filesystem level would be the distant second choice here, as the presence of bad (unrelocated) sectors often hurts read prefetches very badly. The acronyms stand for Automatic Read (Write) Reallocation Enable BTW. I hope this clarifies the matters here a bit. Maciej