A sparse image or sparse bundle question in relation to a NAS

Question

Hi all,
I want to create a sparse image or bundle on my Synology DS713+ NAS to store my iPhoto and Aperture libraries.
The reason for a sparse image or bundle lies in the fact that both iPhoto and Aperture very much like a solid Mac Journal formatted drive to operate on.
Because I use an iMac and a MacBookPro I want these libraries available for both computers, and while they reside on a NAS they are 'automatically' backed up, and acessible to both computers.
I've tried storing the iPhoto library on the NAS directly (not Mac formatted but some Linux format, nót FAT32 anyway), but this was performing very poor (copying the library took hours and hours), and I've read on many NAS and Synology forums that this is not the way to go. The best solution I've read from these forums is to create a Sparse Image or Bundle on the NAS to benefit fully form an iPhoto or Aperture Library.
Now I have created a Sparse Image, and mounted it, and moving (copying) an iPhoto Library to it is done in a snap (amazing).
But having the Sparse Image mounted on my iMac, I cannot acess it on my MacBookPro unless I first umount it on the iMac, and then mount it on the MacBook.
Is there a way that such a Sparse Image can be mounted on more than one computer at the same time. In my case, mounted on both the iMac and the MacBook?
Or must it specifically be a Sparse Bundle to accomplish this, or maybe some Terminal wizzardry to get this done?

Answer 1

I'm a little confused here, but what you did answer did help quite a bit. Thanks for that. Anyway, I'm having problems adding to the array. It keeps telling me 'cannot find symbol - method add (double). I'm assuming that this method should be defined in the AuditRecord class, which has been given to me but there seems to exist no method in that class called 'add'. I suppose I could make one, but my professor said that we shouldn't be modifying the AuditRecord class at all, which leads me to believe I'm on the wrong track again. Anyway, here's my updated code in the hopes that it's a simple mistake that I'm making once again:
public class AuditTrail
    private ArrayList<AuditRecord> auditTrail;
    //ArrayList<AuditRecord> auditTrail = new ArrayList<AuditRecord>();
    //private double amount;
public AuditTrail()
   auditTrail = new ArrayList<AuditRecord>();
* Add a record
public boolean add(double amount)
       if (amount > 0)
       //create auditrecord and add to audit trail (array list)      
       AuditRecord auditTrail = new AuditRecord(amount);
       //auditTrail.AuditRecord(amount);
       auditTrail.add(amount);
       System.out.println("Amount of "+amount+" added.");
       return true;// similar behavior to a collection
    else
        System.out.println("Invalid deposit amount.");
        return false;
}