iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
Probably not. A 4TB SSD does not automatically need 64 KB clusters. Windows uses 4 KB as the default NTFS allocation unit, and Microsoft lists that configuration as supporting volumes and files up to 16 TB. A larger allocation unit becomes relevant when the drive is dedicated to very large files—such as VHDX files over 1 TB—and you can accept the space waste and destructive reformatting involved.
What a cluster size controls
A cluster, also called an allocation unit, is the smallest addressable and allocatable unit in a filesystem. A file consumes whole clusters, so a 1-byte file still occupies one complete cluster. With 4 KB clusters, that minimum is small; with 64 KB clusters, every tiny file can consume substantially more space than its contents require.
Larger clusters reduce the number of allocation units the filesystem must track and are intended for workloads dominated by large, sequential files. They do not create a universal SSD speed boost. Microsoft’s guidance documents formatting recommendations and capacity limits, not a benchmark proving that 64 KB is faster on every SSD.
NTFS allocation-unit sizes and their limits
| Allocation unit | Microsoft-listed maximum volume and file size | Best fit | Main cost |
|---|---|---|---|
| 4 KB | 16 TB | Default NTFS choice; mixed workloads and ordinary Windows volumes | More allocation units for very large files |
| 64 KB | 256 TB | Volumes dedicated to large files, including documented VHDX scenarios above 1 TB | More wasted space for small files; requires reformatting to change an existing volume |
| 2 MB | 8 PB on supported newer Windows versions | Specialized, extremely large-file workloads | Very poor efficiency for small files and narrower compatibility |
These are Microsoft’s current NTFS figures. The actual maximum depends on both cluster size and the total number of clusters supported by NTFS. A 4TB volume is therefore well within the documented 4 KB limit; capacity alone is not a reason to change it.
#1 Best Overall
- Get NVMe solid state performance with up to 1050MB/s read and 1000MB/s write speeds in a portable, high-capacity drive(1) (Based on internal testing; performance may be lower depending on host device & other factors. 1MB=1,000,000 bytes.)
- Up to 3-meter drop protection and IP65 water and dust resistance mean this tough drive can take a beating(3) (Previously rated for 2-meter drop protection and IP55 rating. Now qualified for the higher, stated specs.)
- Use the handy carabiner loop to secure it to your belt loop or backpack for extra peace of mind.
- Help keep private content private with the included password protection featuring 256‐bit AES hardware encryption.(3)
- Easily manage files and automatically free up space with the SanDisk Memory Zone app.(5)
When 64 KB makes sense
Dedicated virtual-disk or archive volumes
Microsoft specifically documents 64 KB allocation units, together with large file-record segments, for NTFS volumes holding large files such as VHDX files larger than 1 TB. This is a specialized design: the volume should not also be expected to hold thousands of small application, profile, or source-code files.
Large sequential media and datasets
A drive used almost entirely for very large video, imaging, backup, or dataset files may benefit from the simpler allocation pattern. The improvement is workload-dependent, so measure the applications that matter rather than assuming a result from the cluster size alone.
Rank #2
- NONSTOP SPEED: Race through projects with our fastest SSD for creators; Load, edit and transfer with sustained read and write speeds of up to 2,000MB/s1; The T9 Portable SSD performs at high speeds even during longer processes
- DYNAMIC THERMAL GUARD: When you’re elbow-deep in a passion project, the T9 Portable SSD stays cool; Its advanced thermal solution withstands and controls heat to keep the SSD at ideal temperatures—even in heavy use2
- ADAPTS TO EVERY NEED: Whether you’re using a desktop, camera or a gaming console3, count on the T9 Portable SSD for extensive compatibility; It’s a true team player when it comes to heavy-duty application usage or file-saving
- STRONG. SOLID. STABLE: From concept to completion – the T9 Portable SSD gives you the longevity to last through heavy use with one convenient drive that dares to go the distance
- WORKS LIKE MAGIC: Your T9 Portable SSD performs like new with the always up-to-date Magician Software; With firmware updates, extra encryption and continual monitoring of your drive health, it works like a charm
When 4 KB is the better choice
- Keep the default 4 KB NTFS setting for a general-purpose Windows SSD.
- Use it when the volume contains operating-system files, applications, documents, caches, and other small files.
- Choose it when you want maximum small-file space efficiency and broad application compatibility.
- Keep it when the existing volume already works; changing allocation units requires backing up and reformatting.
On a 4TB SSD, 4 KB is not an error or an undersized setting. It is the default Microsoft configuration and supports considerably more capacity than the drive contains.
How to check Bytes Per Cluster before changing anything
- Open Command Prompt with administrator privileges.
- Run
fsutil fsinfo ntfsinfo X:, replacingX:with the volume’s drive letter. - Read the Bytes Per Cluster line. Microsoft’s example reports
4096, which is a 4 KB allocation unit. - Record the filesystem type and current value, then verify that every application using the volume supports your planned format.
- Back up important files before making any change.
The command reports the current setting; it does not change it.
Rank #3
- Save time storing and transferring data with powerful NVMe solid state performance featuring up to 2000MB/s(1) read/write speeds.
- A forged aluminum chassis acts as a heatsink to deliver higher sustained speeds in a portable drive that’s tough enough to take on any adventure.
- Travel worry-free with a 5-year limited warranty(2) and a forged aluminum chassis-silicone shell combo that offers a premium feel and added protection.
- Up to 3-meter drop protection and IP65 water and dust resistance(4), and a handy carabiner loop for securing your drive all deliver extra peace of mind when you’re out in the world.
- Easily manage files and automatically free up space with the SanDisk Memory Zone app(5)
What reformatting a 4TB SSD involves
Windows cannot normally convert an existing NTFS volume from 4 KB to 64 KB in place. You must copy the data elsewhere, format the volume with the desired allocation unit, and restore the files. Formatting is destructive. Microsoft’s recovery documentation describes available recovery modes but does not guarantee that deleted data can be recovered, so a backup is a prerequisite rather than an optional precaution.
In the Windows formatting interface, select NTFS and the required allocation-unit size when creating the volume. The exact labels and available choices can vary by Windows version and device. Do not format until you have verified the destination, backup, filesystem, and applications that will access the drive.
Rank #4
- NEARLY 2X FASTER THAN OUR PREVIOUS GENERATION(8) – move 1,000 high-res photos in under 60 seconds(6) with up to 2000MB/s transfer speeds(2).
- IP65 RATING AND UP TO 3M DROP PROTECTION(3) – protects against spills and drops.
- POCKET-SIZED – fits easily in pockets and small bags.
- SPACE TO OWN YOUR AI CONTENT – speed and capacity to download your high-res clips and photo edits.
- 256-BIT AES ENCRYPTION(4) – helps keep private files secure with password protection.
NTFS or exFAT for a 4TB external SSD?
| Consideration | NTFS | exFAT |
|---|---|---|
| Typical use | Windows computers, SSDs, external hard drives, and USB drives over 4 GB | Removable storage shared between operating systems |
| File-size model | Depends on NTFS cluster size; Microsoft lists 16 TB at 4 KB and 256 TB at 64 KB | 64-bit file sizes; clusters up to 32 MB |
| Allocation-unit choice | 4 KB default, with larger documented options for specialized workloads | Workload-dependent; large units favor large sequential files but waste more space with small files |
| Compatibility priority | Best when Windows features and permissions are central | Useful when the drive must move between operating systems |
Choose exFAT for cross-platform convenience only when the devices you use support it. Choose NTFS when the SSD primarily serves Windows systems and you need the filesystem’s normal Windows behavior.
Quick wins for a faster PC:
Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →Quick Recap
A practical decision checklist
- Mixed files or a boot/system drive: use NTFS at 4 KB.
- Dedicated VHDX volume with files above 1 TB: consider NTFS at 64 KB and the associated large file-record configuration.
- Mostly large sequential files: test the real workload before reformatting; do not assume a performance gain.
- Frequent sharing across operating systems: evaluate exFAT and select its allocation unit according to the ratio of large to small files.
- No verified backup: do not reformat yet.
Common mistakes
- Changing a 4TB drive solely because its capacity sounds large. Capacity does not determine the correct cluster size.
- Assuming 64 KB clusters make every SSD faster. The official recommendations are workload-specific, not universal benchmarks.
- Ignoring small files. Larger clusters can consume much more space than the files’ logical sizes.
- Formatting before checking the drive letter and backup. A mistaken target can make recovery difficult or impossible.
- Choosing exFAT without checking the computers, consoles, cameras, or other devices that must read the drive.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
