Hard Drive Cluster Sizes

First off, the available cluster sizes are as follows (in Bytes):

FAT32:  4k, 8k, 16k, 32k

NTFS: 512 B, 1k, 2k, 4k, 8k, 16k, 32k, 64k

But cluster size is influenced by your drive partition size.  However, the huge drives all use the same cluster size:

The 32 GB Factor - determines Cluster Size

FAT32 partitions exceeding 32 GB must use 32k clusters.  NTFS partitions exceeding 32 GB must use 64k clusters.  

Today's drives are huge ! !  And in most cases, even after you partition the drive into smaller logical drives - the logical drives will also exceed 32 GB.  This means the cluster size will be 32k for FAT32 and 64k for NTFS !!!

Setting the Cluster Size During Format

The following tables show the default cluster sizes that are created during the format of a hard drive partition.  There nay be flexibility in this - for example, a 10 GB drive would be formatted with 16k clusters by default, but if you used the /z switch in the command you can override that default and format 32k clusters, for example.

format x: /z:64
    where x= your hard drive letter will format 32k clusters under fat 32.

for other sizes of clusters :

FORMAT x: /Z:n     - where n is the number of 512 byte sectors in a cluster;
    NOTE:  n must be a number 2^x, so: 1, 2, 4, 8, 16, 32, 64, ...

NOTE:   the recent slew of monster drives makes customizing the cluster size impossible.  For these drives, the 32k cluster size is mandatory, since anything smaller than that makes too many clusters.  For huge 300 GB drives and up, even 32k - which will work - is functionally too small as it causes zillions of clusters to be created.  A cluster size of 64k would be more appropriate.

Changing the Cluster Size

Once you have set the cluster size by formatting a drive - it can only be change by:

1. re-formatting the drive (which destroys all data)

2. using Partition Magic to resize the clusters (will keep data intact)

Cluster Size vs Partition Size

FAT12 and FAT16

FAT 16 and FAT32

NTFS

Recommended Cluster Size

*** also see http://www.storagereview.com/guide2000/ref/hdd/file/partCluster.html 

Today's hard drives are HUGE, and therefore in most cases you will be using 32 kB clusters.  This is actually good, though, since the larger the cluster sizes are, that more data that is transferred with each Read and Write to the drive.  If you have a huge drive you should break it up into 2 or 3 smaller logical drives.

WinXP offers you the choice of either FAT32 or NTFS as your hard drive file system.The FAT32 (File Allocation Table) file system is what you used in Windows 98, SE and ME. The NTFS system was first available with Windows NT, then Win2000 and now Windows XP. The NTFS stands for "New Technology File System" just as the NT in Windows NT meant "New Technology". Wow! Anyway, these are two very different methods of organizing and recording information on the files stored on your computer's hard drive. WinXP can use either file system. In fact, you can have both file systems on the same computer and easily transfer files between them.

NTFS can work with single drive partitions up to 8 petabytes, that's 8 followed by 15 zeros. Apparently Microsoft has actually tested NTFS with a 19 terabyte partition (19 followed by 12 zeros). If you have trouble with the large numbers used in hard drive sizes here's a table that might help.

Compare this large drive capability of NTFS with the FAT32 system that is limited to about 2 terabytes. Don't think this may not be a problem? Just remember that we now have drives with more than 200 GB capacity. Terabyte sizes are not that far in the future. FAT32 has other problems as well. As you increase the volume or partition size in a FAT32 system, the cluster size also increases. The cluster size ranges from 4 K to 32 K. You reach the 32K maximum with drives larger than 32 gigabytes, at least according to Microsoft. Some references indicate otherwise. However, the following table is taken from two different Microsoft references on cluster size in FAT32.

The whole point of the cluster size problem is that the minimum file storage space is ONE cluster. Therefore, if you have a 512 K file or a 1 K, it will take up one full cluster. On the 40 GB drives that are now commonly available, that cluster takes 32 thousand bytes (32K) of space. However, the default cluster size with an NTFS partition is 4K even up to the maximum partition of 8 petabytes. So file storage is far more efficient with NTFS. You might say "So What?" with my 80 GB drive why should I worry about file size? That may be true for a while, but there are other efficiencies provided by NTFS as well as some problems if you are converting a FAT32 system to NTFS. As I mentioned, NTFS is a very different filing system than FAT32. Except for very small files, NTFS is much faster in locating files because of its B-tree structure. Now I know this means nothing to you unless you are a programmer. So lets look at this a little. In a FAT file structure each folder entry contains an index into the file allocation table. This identifies the starting cluster of the folder. When you want to load or view a file, the system has to walk the folder structure to get to each segment of the file. First it finds the starting cluster of the folder, then the starting cluster of any subfolder, then the starting cluster of the file, and finally, the clusters that contain the file. In mathematical terms, the average time to find a file using FAT32 is N/2, where N is the total number of files in the File Allocation Table. You can also see that to find the file, the command to load or read the file must contain the complete path (all the directories and subdirectories) that must be searched to find the final file. Not a rapid process, especially when you realize that even a 2 GB hard drive can have 12-15,000 files! I have seen 40 GB drives with over 60,000 files and occupying less than 20 GB of drive space. These were not drives with a lot of data on them. Instead the majority of these are system files created by Windows, Internet Explorer, Outlook/ Outlook Express, etc. They are also program files created during the installation of your applications.