MacOS size weirdness

[Peter Bagnall]

> But part of what puzzles me is that this is occurring on a /brand new/
> installation.  I just reformatted the whole hard drive and did a basic
> installation off a MacOS 9.1 install CD.  I haven't had time to corrupt
> anything.  =)

That's the reason I suspected block size as the culprit. I must admit 
I'm puzzled why the 1Gb disc is reporting 431.2 MB used in total, but 
only 252.5 used by the system folder etc. It seems a remarkable 
coincidence that the size is the same as the size used by the larger 
disc though.

I've just been looking a bit more closely at an HFS standard partition 
using OS X. The command line allows a bit more analysis that you can 
easily do on Mac OS 9. The partition is 1013.9MB, so roughly the same 
size as yours.

If I select everything on the disc and do "get info" I get 350.9MB on 
disk (313,380,894 bytes)
If I select the disk itself I get 373.1 MB on disk (391,266,304 bytes)

That's a diff of 22.2 MB

Now, if I check to see how many blocks are being used from the teminal 
in MacOS X I get

total blocks = 2076640
used = 764192

note: this suggests 512 byte blocks, unfortunately this might not be 
true, the unix tools display things pretending it's 512 byte blocks even 
if your block size is bigger. Doesn't actually matter at for what I'm 
doing, so lets just be naive and believe it, for now...)

Now if I use another tool to see how many blocks are used by files I get 
760096. So the total used is 4096 more than is used by files. That's 
about 2MB. That's ok, that 2MB will be things like the free block map 
and other data structures of that ilk. So that leaves 20.2MB to track 
down.

Ok, now I can list by directory, and on the command line I see loads of 
files that I can't see in the finder, such as Desktop DB, Desktop DF and 
so on.  Summing all the files in that list (that don't appear in the 
Finder) accounts for  41282 blocks which is about 20.2MB, voila!

So my disc checks out ok. BUT, comparing the files sizes in bytes with 
the number of blocks being used there's something odd going on. Every 
file seems to be using a blocks in multiples of 32. Now remember I said 
that unix has a tendency to lie about block sizes in the tool I'm using, 
what that really suggests is that the block size is 32 times bigger than 
it's quoting. That would be a block size of a huge 16kB. On a 1 GB disc. 
There is another possibility, that HFS standard allocated blocks in 16kB 
groups, but that would be rather strange, that is it allocates 32 blocks 
at a time to a file. This tallies with what get info says though. It 
reports 16kB used for a 600 or so byte file. That really does suggest a 
16kB block size, which is frankly much bigger than I would expect.

Just looking for this effect on my HFS+ partition and it seems to have 
4kB blocks which is more as I would expect.
To summarise - it seems that there are a significant number of hidden 
files, which doing a select all and get info will not report, about 20MB 
worth on my disc (which doesn't have a system installed on it). So it 
could be that you're just seeing a lot of hidden files there. It also 
seems that block sizes are bigger than you might have imagined, so the 
amount of wasted space is going to be pretty large. A rough guide to 
this is the number of files on the disc, could you let us know how many 
files there are? Trash is hidden, so emptying that will help. I think 
someone else has mentioned this already. Rebuilding the desktop may also 
change things too, so you might want to try that, cause the desktop DB 
is a hidden file, and I think it can get quite large, although you would 
expect it not to be just after installing!

But all in all, although what you're seeing is annoying, I don't think 
it's actually a cause for alarm. I think your system is almost certainly 
working just fine, it's just that some subtleties of the file system are 
getting in your way. To really get to the bottom of it you're going to 
have to get hold of some tools for MacOS 9 which allow you to see hidden 
files etc so you can really see what it going on. I hope this has given 
you a little peace of mind though.


>   Unless you think this indicates some more serious
> problem--corruption in the formatting itself, or (god forbid) some
> physical problem with the disk.

When you format, the system should mark any bad blocks. A bad block 
indicates a region on the disc which has failed for some reason. A few 
years back it was very common for discs to have a small number of bad 
blocks and no one worried about it. I've not noticed it on any discs of 
mine lately but I think they may be getting better at hiding them.  
Anyway, if there are bad blocks on the disc you should be alerted to it 
if you do a surface scan of the disc. You don't need to worry about a 
few, but if you have lots it's time to change the disc. Lots suggest the 
disc may fail catastrophically in the near future. Discs do all 
eventually die this way, but in recent years many people won't have 
noticed this fact since computers go obsolete long before many discs 
fail on them!

All in all, I doubt this is a problem, but do a surface scan just to be 
safe.


>   I'm probably going to reformat again
> within the next few days, so it's not like this is an installation I'm 
> going to
> be depending on.  But it is hardware I'll be depending on, and I'd like 
> to
> get to the root of this before I reformat, in case it informs the sizes 
> or
> filesystems I choose...

MOL will run off HFS+ ok I believe, but unless someone has finally 
written an HFS+ filesystem for linux it won't be accessible in linux. 
HFS is however accessible in linux as you say. The way I've done this in 
the past is to use an HFS+ partition as my MacOS install, as big as you 
think you will need (also used by MOL). A 2Gb or so HFS partition to 
exchange data with linux, and then the rest in linux partitions of 
various sizes. I did find an extension for MacOS a while ago for 
mounting ext2 partitions in MacOS. I think it was called MountX. It 
worked just fine apart from being VERY slow, but if you can live with 
that it may be of some help to you. It has been a couple of years since 
I tried MountX though, so things may have improved. It was on MacOS 
8.something too so I suggest you check compatibility first too.

You may want to make your MacOS partition larger than 1GB too, I'd go 
for 2-4 GB myself because I'd install software on the HFS+ partition. 
MacOS software is of no use to linux, MOL will be able to use it cause 
it can read HFS+ (cause it uses the MacOS filesystems not the linux 
ones). The only things I'd put on the HFS are the files I wanted access 
to in both systems, which should be ok in 2GB.

Hope this is helpful

Pete