DumbDD

[ironborn65]

I see a lot of enthusiasm here—that’s great.
That said, speaking as a layman, could someone please clearly outline the expected use cases for this “DumbDD” app?

 

[CuriosTiger]

I see a lot of enthusiasm here—that’s great.
That said, speaking as a layman, could someone please clearly outline the expected use cases for this “DumbDD” app?

On UNIX systems, dd is used for writing raw data to a block device (such as a raw SCSI disk) below the file system layer. The applications are numerous. For example, it's a fast way to clone one disk to another (as long as the destination is at least as large as the source.) It's a decent way to exercise every sector of the disk and discover any read/write errors. And it's a way to wipe a corrupted disk, as some types of disk corruption can upset traditional formatting tools.


There are other uses, but those are three that come to mind.

 

[ironborn65]

Thanks mate, I do use 'dd', especially in the past with the previous generation of SCSI emulators; now they use file images instead.
What is the deal with DumbDD?

 

[Phipli]

What is the deal with DumbDD?

Other hard disk imaging programs don't tend to copy the whole disk, only the partitions, so you don't get a copy of the drivers and partition map etc. Also you can't tell them to only copy or write to/ from a specific location.

That's what DumbDD is being made to do.

 

[CuriosTiger]

Thanks mate, I do use 'dd', especially in the past with the previous generation of SCSI emulators; now they use file images instead.
What is the deal with DumbDD?

As far as I know, no such program existed in classic MacOS, except perhaps as part of A/UX. DumbDD is just an app that offers you that same functionality without having to use another computer/OS.

Using file images rather than raw partitions is a convenience ZuluSCSI and the like are offering. That requires additional file system handling (in this case, ExFAT or FAT32 are supported, if memory serves) and some extra code to deal with parsing file names and such. It also comes with a slight performance penalty, although that's probably a non-issue on classic Macs since the limiting factor there is the speed of the SCSI bus.

But inside of that HD0.img file (or whatever you name yours) there's still a classic Apple Partition map, a SCSI driver and whichever partitions you have created. The "file images" abstraction is something you see when you mount the images on a modern computer. It's invisible to classic MacOS. As far as your classic Mac is concerned, that "file" is just a block device with a certain number of sectors.

 

[Snial]

Thanks mate, I do use 'dd', especially in the past with the previous generation of SCSI emulators; now they use file images instead.
What is the deal with DumbDD?

The disk imaging apps on a Mac appear to be too clever, aiming to copy individual volumes and caring about the underlying file system. DumbDD copies sectors from a real SCSI HD, indexed by sector, using the SCSI Toolbox APIs, not the file system FS or PB routines. It can also copy them back from an image.

The primary use case is if you have an old SCSI HD + an old SCSI Mac and you want to copy a foreign partition map and file system into it (which is my use-case).

Also, Thanks @CuriosTiger .