39991: I am using Mac OS 8.1 and when I view files on my Acronis Files Connect server, the file sizes are incorrect. What's wrong?

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Question:

I am using Mac OS 8.1 and when I view files on my Acronis Files Connect (formerly ExtremeZ-IP) server, the file sizes are incorrect. What's wrong?

 

Answer:

This problem is a known bug with Mac OS 8.1 and AppleShare Client 3.8. It's actually the result of an undocumented portion of the AFP protocol.

AFP 2.2, which is the first version to really support AFP over TCP, does not specify a call for the client to get the allocation block size. When the Finder calculates how much space is used by a file (or, specifically, a file fork) it determines how many blocks the file would use. If, for instance, the block size is reported as 32K and you have a file that takes up 1 byte, the Finder will report the size as 32K, because that's how much space on the disk is actually being used.

Anyway, before Mac OS 8.1 - specifically, before the HFS+ file system - the block size was always calculated by dividing the size of the disk by a certain value. That's why HFS (before HFS+) was so bad for large disks - small files wasted LOTS of space. Well, the Mac used this same technique for AFP volumes as well.

But in Mac OS 8.1, the behavior changed. Suddenly, it was possible to have disks with much smaller block sizes. But only after Apple released the OS did they realize that AFP volumes had this problem. So they placed an undocumented call into the AFP protocol for determining the block size. We implemented support for it in Acronis Files Connect.

After Mac OS 8.1 came out, Apple released a new client. While AppleShare Client 3.8.1 probably fixes this problem, it MAY be that the bug is in Mac OS 8.1 itself. Later versions of Mac OS do the right thing.

Upgrades to later Mac operating systems are probably worth it - Mac OS 8.6 and Mac OS 9 are our versions of choice.

 

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