1. Performance: you're adding a layer of indirection, since the dmg is a file on the "real" filesystem, reading or writing a file to it requires altering a file on another file system. This is not very fast; and while it may be "fast enough" for some things, it won't be for others.

You would be hard pressed to find a scenario where this difference was even measurable. When it comes down to it they are both exactly the same thing, a series of blocks on a disk. The fact that you might have to do one extra lookup to find out where those blocks reside is fairly meaningless in the real world. There are plenty of other situations where people routinely add one (or more) levels of disk indirection on production systems (LVM and RAID for example).

2. Reliability: if a disk gets a bad sector, the worst case scenario is that the data on that sector is lost. If a DMG file gets corrupted, that whole "disk" is damaged, often beyond repair.

From the point of view of both the operating system and the data contained on the disk, there is no difference between a filesystem on a physical disk and a filesystem on a disk image. If you lose a block of data on either one, the effect is going to be identical regardless of whether it was a physical disk or not. The tools you would use to recover from losing a sector on a physical disk will work exactly the same on the disk image.

www.jasonkohles.com
We're not surrounded, we're in a target-rich environment!

In reply to Re^4: (OT) Fixing OSX's biggest weakness as a dev platform by jasonk
in thread (OT) Fixing OSX's biggest weakness as a dev platform by dragonchild

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