how to calculate correctly the cluster size

[Sylwia]

Hi!

I need Your help...

I am trying to find a way to calculate the cluster size for a drive. I
looked at the GetDiskFreeSpaceEx function in Win32 and it turned out
that it didn't provide the information I was looking for.
Using the old GetDiskFreeSpace function I could just multiply the
Bytes per
Sector by the Sector per Cluster and get the cluster size. I heard
that the old GetDiskFreeSpace function may report not proper values
for volume sizes that are greater than 2 gigabytes. The new version of
that function (GetDiskFreeSpaceEx) returns the final disk free size
without the ability to calculate the cluster size - and the old
version does not work correctly with FAT 32... what can I do? Is there
another function I can use?

Thank You in advance,

Farraige

 

[Josiah Carlson]

I am trying to find a way to calculate the cluster size for a drive. I

looked at the GetDiskFreeSpaceEx function in Win32 and it turned out
that it didn't provide the information I was looking for.
Using the old GetDiskFreeSpace function I could just multiply the
Bytes per
Sector by the Sector per Cluster and get the cluster size. I heard
that the old GetDiskFreeSpace function may report not proper values
for volume sizes that are greater than 2 gigabytes. The new version of
that function (GetDiskFreeSpaceEx) returns the final disk free size
without the ability to calculate the cluster size - and the old
version does not work correctly with FAT 32... what can I do? Is there
another function I can use?

Generally, I believe sectors are consistantly 512 bytes, and depending
on the format of your drive, cluster size can vary. Both NTFS and FAT32
generally run with 4k clusters, and at least until mid-2002, there
didn't exist a commercial defragmenter that could handle non-4k clusters
in Windows (I had a drive with 16k clusters that I needed to repartition
in order to fix that, thank god for partitionmagic). I don't think you
would be out of line to assume 4k clusters on installations using FAT32
or NTFS.

In terms of volume sizes > 2 gigs, that sounds like the old cluster size
and addressing limit for FAT 16, but considering how rare FAT 16 is
nowadays (perhaps pre Win95 OSR2 installations still use it), I wouldn't
worry too much (unless you are specifically writing for old operating
systems).

- Josiah

 

[Dennis Lee Bieber]

in order to fix that, thank god for partitionmagic). I don't think you
would be out of line to assume 4k clusters on installations using FAT32
or NTFS.

Heh... Checking just two of my 10 partitions (spread over two
internal drives, and an external FireWire) I'm running 8K clusters, and
likely much larger on the FireWire (which has four 40GB partitions!).

W98se/FAT32

--

 

[Josiah Carlson]

Heh... Checking just two of my 10 partitions (spread over two
internal drives, and an external FireWire) I'm running 8K clusters, and
likely much larger on the FireWire (which has four 40GB partitions!).

W98se/FAT32

Can you defrag your disks? If so, then perhaps my not being able to
find a software to defragment disks was a 'feature' of using Windows
2000, NTFS and non-4k clusters.

I'm curious; did you set the cluster size yourself, or were those
automatic sizes generated by 98SE?

- Josiah

 

[Dennis Lee Bieber]

Heh... Checking just two of my 10 partitions (spread over two
internal drives, and an external FireWire) I'm running 8K clusters, and
likely much larger on the FireWire (which has four 40GB partitions!).

The FireWire is running 32K clusters on each of the four
partitions -- smallest size possible on the partition (and conversely,
about the most optimum partition sizes too).

--

 

[Dennis Lee Bieber]

Can you defrag your disks? If so, then perhaps my not being able to
find a software to defragment disks was a 'feature' of using Windows
2000, NTFS and non-4k clusters.

The big partitions, about monthly (actually, all partitions
about monthly). The most used data partitions (smaller) about weekly.

I'm curious; did you set the cluster size yourself, or were those
automatic sizes generated by 98SE?

These are all FAT32 partitions. Don't know how to, if possible,
change clusters on my XP laptop using NTFS.

While I used Partition Magic to do the partitioning, the sizes
are the smallest cluster size possible in the partition size. One reason
I have so many partitions:

30GB (raw) drive:
C: 9GB System software
E: 1GB swap/temp
F: 15GB games and downloaded files
plus two ext2fs Linux partitions

40GB (raw) drive:
D: 5GB 3rd party application software
G: 7.5GB Text data (Agent data, Word, database,
etc.)
H: 15GB Graphics (digicam images, scans, etc.)
plus two more ext2fs Linux partitions

The FireWire drive has three 44GB partitions (maximum for W98se,
I believe), and a 21GB partition). Used for MP3s and some miniDV
captures.

It took forever to defrag a 300GB (two partitions) firewire
drive under NTFS (this drive is used with my XP laptop for miniDV
captures and editing). I actually had to double the memory of my laptop
(now 768 MB) before the defrag could run to completion.
--

 

[Josiah Carlson]

These are all FAT32 partitions. Don't know how to, if possible,

change clusters on my XP laptop using NTFS.

While I used Partition Magic to do the partitioning, the sizes
are the smallest cluster size possible in the partition size. One reason
I have so many partitions:

The Windows 2k "Disk Administrator" software for 2K always uses 4k
cluster sizes by default. I believe your varied cluster sizes are the
result of using Partition Magic to create them.

It took forever to defrag a 300GB (two partitions) firewire
drive under NTFS (this drive is used with my XP laptop for miniDV
captures and editing). I actually had to double the memory of my laptop
(now 768 MB) before the defrag could run to completion.

There exists an algorithm for defragmenting a drive that only needs to
read and write the entire drive twice (I wrote one for a database
defragmenter), and there likely exists one that reads and writes even less.

If you have a 150 gig drive (and it is filled), your computer will need
to read and write a around 600 gigs (read, write, each twice, 150 gigs).
Even if your drive is fast, like say 30 megs/second (probably on the
high-end for defragmenting), 600,000/30/3600 ~ 5.5 hours. In reality,
you're probably getting closer to 5-15 megs/second during a defragment,
which would give you 11-33 hours to defrag each of your 150 gig partitions.

It's the whole capacity vs bandwidth issue on hard drives, which is
similar to the bandwidth vs latency issue with RAM. Ahh, technology.

- Josiah