> For the complete documentation index, see [llms.txt](https://docs.foundryosd.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.foundryosd.com/foundry-osd/media/update-usb.md).
# Update a USB drive
Update a Foundry USB drive to apply your current options and the current Foundry applications without erasing the Windows images and driver packs it has already downloaded.
When the selected drive is a Foundry USB drive, the button reads Update USB. Its arrow offers Recreate without cache.
{% hint style="warning" %}
**Update USB** asks for no confirmation. Once the build is ready, the **BOOT** partition is formatted and written again. Check the selected drive before you select the button.
{% endhint %}
## Before you start
* No row of [Start](/foundry-osd/media.md) is marked **Needs attention**, and 20 GB are free on the drives listed in [Start](/foundry-osd/media.md#before-you-start).
* Close File Explorer windows and other programs that use the drive.
* Move away any file you copied to the **BOOT** volume yourself: it is erased.
## Update the drive
1. Connect the drive, open **Start**, and select **Refresh** in the **USB target** card.
2. Select the drive and check that the button reads **Update USB**. This label is the only sign that Foundry OSD recognized the drive.
3. To format **BOOT** completely, expand the **USB target** card and set **USB format mode** to **Full format**. The update then takes longer. **USB partition style** is ignored: an update never changes it.
4. Select **Update USB**, not its arrow: the arrow offers **Recreate without cache**, which erases the drive and its downloads. See [Create a drive without cache](/foundry-osd/media/create-usb.md#create-a-drive-without-cache).
5. If a dialog titled **Update Foundry OSD before creating boot media** opens, apply the update first or select **Create anyway**.
6. Keep the drive connected until the dialog is titled **USB media updated** and reads "Boot volume: X:. Cache volume: Y:.", with the two drive letters.
## How Foundry recognizes the drive
The drive must have an NTFS volume named `Foundry Cache` and its **BOOT** partition. If the cache volume was renamed, the button reads **Create USB**, and creating the drive erases everything, downloads included. If only **BOOT** was renamed or reformatted, the button still reads **Update USB** but the update stops with "Selected USB media is not a Foundry USB media.".
## What an update replaces and what it keeps
| Replaced | Kept |
| ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| The whole **BOOT** partition: boot files and the boot image, with your current options | `Cache\OperatingSystems`, `Cache\DriverPacks` and `Cache\Firmware`: the downloads of earlier deployments |
| Foundry Connect, and the post-installation application with Domain Join, in `Runtime\` on the cache partition | The copy of Foundry Deploy downloaded by an earlier start, reused only while it is the version of the updated drive, `Logs\`, and any file you copied to the cache partition |
| The custom images, post-installation content and custom driver sets of the current configuration, added to the cache partition, except while the [network cache](/foundry-osd/network-cache.md) is on | Custom images and post-installation content written by earlier builds. They keep using space. |
| The driver sets that the new media no longer uses, removed from `Cache\DriverPacks\Custom\`, all of them when no set is left | The downloaded driver packs in `Cache\DriverPacks` |
New custom images, post-installation content and driver sets are copied before **BOOT** is formatted, and Foundry OSD checks first that the cache partition has room for them, before it removes anything. If the update does not fit, [create the USB drive](/foundry-osd/media/create-usb.md) again. See [Custom drivers](/foundry-osd/customization/custom-drivers.md#update-a-usb-drive).
## Check the result
Eject the drive, start a test device from it, and check that Foundry Connect opens, then Foundry Deploy, with the options you changed.
If the update ends with "Unused custom driver sets could not be removed from the USB drive.", it still succeeded: see [Custom drivers](/foundry-osd/customization/custom-drivers.md#update-a-usb-drive).
## Limits
* The boot files must fit the existing **BOOT** partition. Foundry OSD checks this before it formats. If they do not fit, reduce the drivers or [create an ISO](/foundry-osd/media/create-iso.md).
* An update cannot change the partition style or repair a damaged cache partition. Delete the **Foundry Cache** volume in Windows Disk Management, then [create the drive](/foundry-osd/media/create-usb.md) again: creating it erases the whole disk.
* A canceled or failed update can leave **BOOT** incomplete. Run the update again before you use the drive.
## Related
* [Create a USB drive](/foundry-osd/media/create-usb.md)
* [What each media type carries](/foundry-osd/media.md#what-each-media-type-carries)
* [Media creation troubleshooting](/troubleshooting/media-creation.md) and [USB drive and device start](/troubleshooting/media-creation/usb-drive-and-device-start.md)
---
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