How to Fix and Recover Unallocated Space on USB/SD Card

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Applies to: USB drives, SD cards, flash drives, and other removable storage devices

Issue: USB/SD card stops working and shows as unallocated

Have you ever encountered the issue where your SD card or USB drive suddenly shows up as unallocated and even stops working? As a result, you're unable to access the data on it, nor can you save new files. Many users have reported that their used storage devices like hard drives, USBs, SD cards, or flash drives disappear from File Explorer and are marked as “unallocated” in Disk Management, which is very confusing and frustrating.

What is the Unallocated Space on my USB/SD Card?

“Unallocated” refers to the space on a storage device that has not been formatted or partitioned, and therefore cannot be used for data storage. You cannot access unallocated space from within your computer's drive, nor can you write data to it. To use unallocated space, you can either create a new partition with the space, or add it to an existing partition.

When will I see unallocated space?

As mentioned above, the space unallocated on a Windows partition is referred to as “Unallocated Space”. Hence, the space on a freshly initialized disk or the remaining free space will show as “Unallocated”. Existing partitions on a hard drive, external hard drive, USB, SD card, or any other removable disk may also turn into Unallocated Space after certain operations.

Why does a USB/SD card suddenly become unallocated?

The most common reason is accidental deletion or a virus attack. For example, you might have deleted the partition on your USB by mistake, or some program did it for you. It can also happen if you were performing an operation that required deleting partitions without being aware of it. Additionally, it wouldn't be surprising if a malicious virus attack caused various negative effects, including making your USB unallocated.

In most cases, data loss happens along with the partition becoming unallocated. Luckily, you can easily fix unallocated USB or SD card and recover files.

How to Fix and Repair Unallocated USB/SD Card

Depending on whether you need data recovery, different solutions are available for you to choose from.

Method 1: Create the Partition Directly

If the USB device is new, or if you don't intend to recover data from it, you can simply create a new partition with the entire available space to make it usable.

Create a partition on the unallocated space on a USB/SD card:

Step 1: Connect your USB/SD card to the computer.

Step 2. Right-click on "This PC" and select "Manage" > "Disk Management".

Step 3: Right-click on the “Unallocated” space and select “New Simple Volume”.

Step 4: Follow the wizard through its remaining steps.

Create a new partition on the unallocated space

Method 2: From an Unallocated USB Recovery Partition

However, if you attempt to fix an accidentally unallocated USB or SD card that contains important files, you should perform data recovery first.

To recover both files and partitions on a USB drive at the same time, you can use a partition tool - AOMEI Partition Assistant for partition recovery. It can help you restore data and partitions from unallocated space on your USB or SD card, so you don't need to create a volume manually. (Or you can choose to only recover data from unallocated space first, then create a volume as needed.)

Repair Unallocated Space on USB/SD Card:

Step 1. Connect the external storage device to the computer for lost partition recovery. First, click “Partition Recovery” from the left pane. Then select the target disk and hit “New Scan”.

Step 2. Partition Master will run in “Quick Scan” and “Full Scan” modes to search for and display all existing and lost partitions on the selected disk.

Double-click a partition to preview its content.

Step 3: Select the partition with "Lost" status and then click "Recover".

Step 4: Wait for the software to finish the final recovery process, then click "Done".

Step 5: In the "Partition Management" section, your lost partition should now reappear in the drive list.

Knowledge Base: The Difference Between Unallocated Space and Free Space

The “Unallocated Space” and “Free Space” seen in Disk Management are both unused spaces. When you shrink a logical partition, you get Free Space; when you shrink a primary partition, you get Unallocated Space. From the above information, we can easily draw the conclusion that they are the same – the so-called “Unallocated Space” and “Free Space” are actually “unallocated” space.

Additionally, free space can refer to unused space on an existing partition, disk, or external storage device. This is different from blocks marked as “free space” in disk management, which are available for use.

Bottom line

In short, you can fix an unallocated USB/SD card/flash drive by creating a new partition. One thing you need to consider is whether you need to recover data from the unallocated space. If so, you can use tools like Partition Master to recover the partition (with data) or Data Recovery Wizard to restore data only from the unallocated removable disk.