"virtual drive" on mac?

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Level 1

11 points

"virtual drive" on mac?

I have a RAID and XSAN 1.2, and I want to create a "virtual volume" similar to using the MOUNT command in Windows, where a volume (aka "drive letter" in Windows) actually points to a folder within a real volume.

I've been looking into Symbolic Links and /etc/fstab.

But it's all new to me and I don't want to mess things up, esp with XSAN and all.

Can anyone explain how I might use one of these methods to make a folder within one of the volumes on the RAID appear on the desktop/finder as an actual volume?

I was thinking to create a symbolic link within the /volumes folder which points to the "destination" folder. Let's say one of the RAID volumes is called "Media", which has a folder called "A" at the root, and a folder called "B" within "A" ... can I create a symbolic link in /volumes like this:

cd /Volumes
ln -s /Volumes/Media/A/B/ VolumeB

I would hope this would make the Finder "see" a new volume called "VolumeB", which would actually reside within "Media". But is this dangerous?

Or is there a way to do it in the fstab file?

I would like my virtual volume to appear on the desktop/finder, specifically to be visible to Avid as another usable volume. And I want this volume to only appear on the machine where I set it up; that is, I don't want it to appear to any other machines connected to the RAID.

I am completely new to Unix/terminal, so any guidance is greatly appreciated. (Assume I'm an idiot!)

thanks!

G5, Mac OS X (10.4.5), XSAN 1.2, Avid Xpress Pro 4.8.4

Posted on Apr 27, 2006 2:49 PM

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Answer 1

Apr 27, 2006 6:14 PM in response to Ze'ev

many hdiutil is what you need.

hdiutil create -size 100m -volname test-image -fs HFS+ -o test.dmg
................................................................................ ...............................
created: /tmp/test.dmg
%hdiutil attach ./test.dmg
/dev/disk1 Apple partitionscheme
/dev/disk1s1 Apple partitionmap
/dev/disk1s2 Apple_HFS /Volumes/test-image

or you can just double click the dmg from the finder.

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Answer 2

reese_

Level 4

1,735 points

Apr 27, 2006 6:37 PM in response to Ze'ev

Why not just make an alias to your desktop of the your target volume? Then it will appear on the desktop. To save there from within an App use the keystroke cmd+d and then select the alias. If the server is not mounted and you access the alias the OS will try to mount it and prompt for passwords as necessary.
You can also put the alias in the side bar, then when saving click on the folder and you are there.
Be careful while working in /Volumes. It's used by the system and tends to clean itself up.

Reese

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Answer 3

Ze'ev Author

Level 1

11 points

Apr 28, 2006 3:31 AM in response to Nils C. Anderson

many hdiutil is what you need.

hdiutil create -size 100m -volname test-image -fs
HFS+ -o test.dmg

The problem with this method is that I have to pre-determine the size of the virtual volume.

Let me correct what I said earlier -- it's not MOUNT in DOS; it's "SUBST", e.g., "SUBST X: D:/somefolder" and I have a new drive called X: which actually resides on D: and has the same free space as D:

I also tried creating a r/w disk image with Disk Utility, but again I have to pre-set the size; and Avid doesn't recognize it as a valid media drive anyway, since it appears as a CD or other removable...

I can't belive there's no way to accomplish in OSX what I can do on Windows with one simple DOS command!

In short, is there an equivalent to SUBST in Unix/OSX?

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Answer 4

Apr 29, 2006 8:35 AM in response to Ze'ev

I'm not familiar with SUBST in DOS, so is this how it works?

1) when you first create the X "drive", it is empty, and its free space is the same as the free space on D (just repeating what you already said)

2) if you then create a new file on D, the freespace of both D and X go down, and are still the same

3) if you then create a new file on X, the freespace of both D and X go down, and are still the same.

4) the file you created on X can or can not be seen on D? (as a file somewhere in D:/somefolder)

Anyway, I've never heard of a unix utility that creates a disk image that behave like that, and I've been using unix for some 15 years. Doesn't mean it doesn't exist -- there is a lot about unix I don't know, and I'm not a professional sysadmin.

When you mount an OS X disk image (file), it also appears on the unix side under /Volumes, and probably also in /dev (I've never checked).

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Answer 5

Ze'ev Author

Level 1

11 points

Apr 29, 2006 1:40 PM in response to Don MacQueen1

I have found a solution, but I am hoping there's a more elegant way to do it.

I installed SharePoints on each machine; then set up a unique share on each machine, with SMB access, so that each machine had a share to its own private folder on the RAID; then enabled Windows Sharing. Then I mount the so-called remote share through the same machine, by doing Connect to SMB://thismachine. The "share" appears as a network volume, even though the machine is sharing "with itself."

As far as I know, SharePoints is just a GUI front-end to simplify doing certain things that can be done with more expert knowledge of OSX/Unix. So is there a way to do this without SharePoints?

And is there a way to do it without "faking" as a share through SMB? I just wonder if that will reduce performance/bandwidth from the RAID.

I suspect there is a way to get that "network volume" to appear without going through "loops." To somehow get that mountpoint (?) to bind directly...

The AUTOMOUNT command looked promising, but my Unix isn't good enough to make sense of the jargon in the manual.

A friend said on Linux you use something with "--bind", but that doesn't work on OSX-flavor Unix.

P.S. to Don: Yes, to all your questions. You got it. And yes, the file in X appears in the corresponding directory. X is just a volume that points to a folder within an actual volume, where that folder is the "root" of X.

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