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The ultimate tweak: Windows Vista or XP installs on larger than default allocation sizes. Even 64KB cluster size. Lesser fragmentation. Make your drive perform like RAID.

The choice of cluster size has an impact on real-world performance, though for most people it is not all that significant. In a nutshell, larger clusters waste more space due to slack but generally provide for slightly better performance because there will be less fragmentation and more of the file will be in consecutive blocks. This occurs because when clusters are larger, fewer of them are needed than when they are small. A 10,000 byte file would require three 4 kiB clusters but only one 16 kiB cluster. This means this file will always be in a contiguous block if stored in a 16 kiB cluster, but could be fragmented if stored in a 4 kiB cluster size partition. The slack tradeoff is a waste of 4 kiB more storage in the case of the 16 kiB clusters, but, this is hardly an issue now with the gargantuan sizes of hard drives nowadays. Small cluster sizes also have a negative effect on partition because they require larger file allocation tables, to manage their much larger numbers of clusters.

Due to this advantage on real world performance of larger cluster size, many have tried to install windows on partitions with cluster sizes larger than 4kb but to no avail. Windows will not allow installing itself on a partition with a cluster size larger than the default allocation size of the NTFS file system... but there is a way around this. Though you cannot use anymore system restore and windows backup, and the installation disk for repairs but who uses them anyway. And who cares when your drive works like RAID.

Five years ago, I have tried for weeks to install Windows XP on a drive formatted with 64KB cluster size with no success. I have searched the net for related articles on how to install Windows on a 64KB cluster size drives or partitions and I found nothing. Okay, let’s cut to the chase, I know you’re itching to do this. Here’s how it works:

1.Partition your drive so that it has two volumes. The first partition you set as the physical volume must be 10 MB or larger and format it with FAT32 or NTFS file system with default allocation size. You should create this partition first because this will become your boot drive and you would want it to be on outer most part of the disk for performance reasons and label it as BootDrive or SystemDisk (any label would do).
2.Create another partition and format it with the NTFS file system with a cluster size of 64KB or 32KB or 16KB, whatever you prefer, but for better performance larger means better as it means less fragmentation and lesser head movement. Label the partition as OSDrive, Windows or anything.
3.Run your windows installation disk. When the installation prompts you to choose which drive or partition you may want to install Windows, choose the second partition you made and it works like magic. It's that easy.
And, oh, besides the two partions that I have told you to create, you might want to hide first your other drives or partitions before installation, or better disconnect it, as Windows might install its system files on those disk if those drives or partitions have default allocation sizes. This tweak also works on Vista. Enjoy!

<snip by jbennet>

Edited by jbennet because: Removed link to blog. Keep it onsite. Jbennet returned and snupped link to email.
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Nice practical tip from — preformatting an NTFS volume with a larger allocation unit and then installing Windows onto that volume can work, but it isn’t magic: Windows by default uses a 4 KB allocation unit on typical volumes and the Format utility won’t pick a larger cluster size unless you explicitly override it. () NTFS itself supports larger clusters (historically up to 64 KB on older Windows builds and larger on newer releases), so the trick is less about “forcing Windows” and more about preparing the disk so setup puts boot files and OS files where you expect. (learn.microsoft.com)

Practical safety points that avoid the usual pitfalls: make the boot/system area a separate, standard-formatted partition (or disconnect other disks) so Windows won’t scatter boot files to another drive during setup — many support threads and Microsoft guidance recommend disconnecting extra drives during a clean install to keep the installer from placing system files on the wrong disk. (learn.microsoft.com) If you do preformat an OS partition for large clusters, use the Format switch to set the allocation unit explicitly; e.g.:

format X: /FS:NTFS /A:64K /Q

(or use DISKPART/PE to do the same). (ftp.zx.net.nz)

Important trade-offs and gotchas: NTFS compression is not available when the allocation unit is larger than 4 KB, so expect compression features to be disabled on that volume. () Volume Shadow Copy / System Restore behavior can also change depending on cluster/granularity — Microsoft recommends thinking about 16 KB+ clusters for heavy VSS usage to avoid excess copy-on-write growth during defrag/backups. (itprotoday.com) For certain server workloads (SQL Server/Exchange) a 64 KB allocation is a documented best practice for data/log volumes — that’s why you’ll see this approach in database tuning guides. (studylib.net)

Bottom line: the method outlined is feasible and used in real deployments, but it’s a deliberate trade: benchmark your workload, verify your backup/recovery and rescue media can read the volume, and keep a small, default-formatted system partition or disconnect other disks during install to avoid boot problems (thanks for the moderation note, @jbennet).

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