Partitoning and capacity loss.

[GPO]

I'm thinking of getting two 80gb hard drives formatted
with NTFS and set up with four partitions on each. Before
I do this I want to know how much capacity this
partitioning is going to chew up.

For example, with just the one partion you have 80 gb
(depending on the manufacturer's definition of a gb). With
two partitions you are presumably going to have an overall
capacity of something less than 80 gb - say 77 gb (or
whatever). How much overall capacity will there be with
four partitions.

 

[Pat [MSFT]]

For each partition, you will have a separate MFT file. This will likely be
the biggest overhead (there are some other items, but they don't amount to a
lot).

The way NTFS lays out a partition is basically the MFT File _reserves_ 1/8
of the volume. In the case of the 80GB, that's 8GB. The filesystem will
avoid placing any data in this reserved area so that the MFT file can grow
without fragmenting. If disk space runs low, then the reserve is released
back to the filesystem for data storage (and consequently the MFT may
fragment). Since the MFT cannot be a size 0, each instance will take up
some room (even with no data on the volume). So we are talking about a few
MBs of loss to overhead.

Pat

 

[GPO]

Thanks for that. What's an MFT file?

For each partition, you will have a separate MFT file. This will likely
be the biggest overhead (there are some other items, but they don't amount
to a lot).

The way NTFS lays out a partition is basically the MFT File _reserves_ 1/8
of the volume. In the case of the 80GB, that's 8GB. The filesystem will
avoid placing any data in this reserved area so that the MFT file can grow
without fragmenting. If disk space runs low, then the reserve is released
back to the filesystem for data storage (and consequently the MFT may
fragment). Since the MFT cannot be a size 0, each instance will take up
some room (even with no data on the volume). So we are talking about a
few MBs of loss to overhead.

Pat

 

[Pat [MSFT]]

MFT == Master File Table

It contains information about the files on the disk. Things like the
pointers to the files on the disk (if the file < 1k, the file is actually
embedded into the MFT to speed IO).


Pat