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Subsituting an external hard drive for a DVD

Last response: in Mac Os X
December 16, 2009 6:45:08 PM

Need to substitute a USB hard drive in place of a DVD, transparently to an appl, running on a Macbook Pro. The data is The Complete National Geographic, about 40GB in size. I have done this on a PC with the subst command in a batch file. How to do the same with a Mac?
December 18, 2009 8:00:50 PM

So you have a disk image of the DVD on an external HDD?
December 19, 2009 10:30:55 PM

Thanks for the reply - I was starting to wonder, 70-some views but no help.

No. It's not what you would call a disc image. There are 6 DL discs in The Complete National Geographic set (all pages of NG since 1888). A little over 40Gb total size. They expect users to swap the discs in & out - scratching them up and generally being inconvenienced. I copied all of the discs to a USB HD, just a standard folder copy, not an image. I want to tell the computer to look at the HD instead of expecting to read the discs from the DVD drive. TCNG also sells the complete set on a HD both for PC's in NTFS format and for OS X I assume with HFS+J format - but I asked their TS and they are no help. I am giving the set to my daughter, but also a hard drive and I want to set it up for her convenience. I haven't used a Mac since college - 25 years ago. I'm a PC power user - used to be a TS geek on PC's. Doing this on a PC is easy - just write a batch file and use the subst command followed by calling the appl - which tells the OS to substitute the hard drive for the DVD. I need something like that for the Macbook. The drive is presently NTFS format - I assume I'll have to use a Mac to format the drive, and read and copy the DVD's again. But I need to know what I need to do, to tell the Mac to look at the USB drive instead of DVD's and launch the front end appl.

BTW they suggest you put the discs in the "cache folder" which is on the boot hard drive, with OS X defined to be /Users/username/Library/Preferences/
Local Store/cache

Fine - and this idea works with a PC with the appropriate path in the Documents and Settings folder - I assume it works with a Mac. But putting it there assumes you have 50GB of space available on your boot drive. I don't want to make that assumption on my daughter's Mac.
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December 20, 2009 5:41:34 AM

There's no equivalent to the "subst" command on OS X, because there's no drive letters. Everything is considered to be part of one file system and you mount and unmount drives as subdirectories (using the commands "mount" and "umount").

It sounds to me like you just need to create subdirectories (or a subdirectory) at the appropriate place and put the data there. Where that appropriate place is is difficult to tell without seeing the application.

Lack of disk space on a particular drive is no probem. You can create a symbolic link (using the "ln" command) to another physical disk.

A shell script to do all this would be easy, but it's not something that could easily be explained here. Read up on UNIX commands and shell scripting; it is much, much more versatile than batch files on PCs.
December 20, 2009 3:12:13 PM

Thanks for your reply. 15 years ago I was a Oracle DBA for AT&T, and before that a programmer. This was on UNIX boxes. After that I was a Sr Engineer on UNIX platforms, supporting client-server databases for Sybase also on UNIX platforms. After I was laid off over 10 years ago, I haven't touched UNIX since.

Anyway, I can bone up on it and look into a shell script. The problem for me is, I'm running out of time, don't have a platform to test this on, and I'm really busy with other business so can't spend the time this will take - including driving 30 miles over to the Micro Center and using one of their Macs. I was hoping one of you experts could tell me exactly the script that should work, and the steps for my daughter to set it up on her Macbook - and what I can do to help her. This has to go in the mail tomorrow or it will be late - and my day today is already more than booked. Might be I could go to the micro center and format the drive and load the data on it so the hardware can be mailed, and work on the script during the week & email it. But then I couldn't test it.

As I said - I know pretty much diddly on using / supporting Macs.

Thanks for your help so far. If you have time to bang out a script that should work, and tell me how to set it up so it's executed on a Mac, with launching the front end appl [TCNG viewer executable filename] - I will be really grateful FWIW. Thanks much.

Best solution

December 20, 2009 4:05:17 PM

The installation actually seems fairly straightforward, following the instructions in the FAQ. Your only problem seems to be the 50GB free space on the drive where the user's folder is located. I would try the following:

1. On a disk where you have enough free space, create a folder, lets, call it "Folder".

2. Open a terminal and find the folder (I think it should be in "/Volumes/<diskname>").

3. Create a link from the user's home directory with the command "ln -sf /Volumes/<diskname>/Folder /Users/<username>/Library/Preferences/

4. Try following the instructions for the HD install.

That's the best I can suggest without the application to hand. (If you need more details of the "ln" command do a "man ln".)

nb. The command in 3.) should be all on one line!