Owners of Xiaomi Redmi 9 often face a shortage of internal memory, especially if the model is purchased with a minimum volume (32 GB). One solution is to combine the microSD card with the main storage, which allows you to use it as part of the system memory. However, this process has nuances, from choosing the right format (Adoptable Storage) to losing the ability to retrieve the drive without losing data.
In this article, we will look at all the steps from map preparation to alternative ways to expand memory if standard unification is not available, learn which Redmi 9 supports the function (including Redmi 9A/9C/9T modifications), how to avoid formatting errors, and what to do if the system does not see the microSD.
⚠️ Important: The process is irreversible — once combined, the card can’t be used in other devices without completely erasing data. If you often move microSD between gadgets, consider alternatives like manual file transfer or cloud storage.
What is Adoptable Storage and how does it work for Xiaomi Redmi 9?
Adoptable Storage is an Android technology that allows you to format a memory card as part of internal storage. Once combined, the system perceives the microSD as the second partition of memory on which you can install applications and save data. On Redmi 9 (with MIUI 12 and later), the function works stable, but has limitations:
- 🔹 The card must be high speed (class) UHS-I/U3 or higher, otherwise the applications will slow down.
- 🔹 MicroSD cannot exceed 256 GB (limited) MIUI).
- 🔹 After formatting, the card cannot be removed without resetting the phone settings.
- 🔹 Some system applications (e.g. Google Play Services) are not portable to shared memory.
Technically, the process converts the card file system to ext4 or f2fs (depending on the Android version), making it unreadable on other devices, while reducing read/write speeds by 10-30% compared to the internal memory of eMMC 5.1, which is equipped with Redmi 9.
If your goal is simply to store photos, videos or music, conventional formatting as a portable drive (FAT32/exFAT) is sufficient.
Preparation of a memory card: requirements and verification
Before combining, make sure your microSD meets the minimum requirements:
| Parameter | Minimum value | Recommended value |
|---|---|---|
| Class speed | Class 10 | UHS-I (U3) or A2 |
| Volume. | 8GB | 64–128 GB |
| File system | FAT32/exFAT | It will be re-formatted to ext4. |
| Recording speed | 10 MB/s | 30+MB/s (for smooth application operation) |
To check the speed of the card, use applications like the A1 SD Bench (available on Google Play). If the write speed is below 15 MB/s, the applications on the combined drive will slow down.
☑️ Preparation of a memory card
⚠️ Note: If the card was previously used as internal memory on another phone, it must be formatted completely via a PC (e.g., utility). SD Otherwise, Redmi 9 may not offer the option of combining.
Step-by-step: how to combine a card with memory
It takes 5-10 minutes to process, and follow the instructions carefully, and after confirmation, all data on the map will be erased.
- Insert a microSD into a Redmi 9 slot. If the phone supports two SIM + microSDs, use the SIM 2 slot.
- Go to Settings → Memory (or Settings → Storage in new versions of MIUI).
- Tap by the name of the card (for example, SD-map: 128 GB) and select Settings (cog in the upper right corner).
- Click Format as internal memory. The system will warn you of data erasure, confirm the action.
- After formatting, select Transfer Data if you want to move some applications to the map immediately.
If the item is not formatted as internal memory:
- 🔹 The card is incompatible (too slow or damaged).
- 🔹 The phone already uses a combined card (you can check in Settings). → Memory).
- 🔹 Installed custom firmware without support for Adoptable Storage.
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If applications are slowed down after combining, return them to internal memory through Settings → Apps → [Select App] → Storage → Change.
What to do if the association function does not work
If Redmi 9 doesn’t offer to format the card as internal memory, try these methods:
- Update MIUI to the latest version. In older builds (below MIUI 12.0.3), the function may have been disabled.
- Check the card on another device. If it's not defined or it's slow, replace it.
- Use ADB (for advanced users). Connect your phone to your PC, activate USB Debugging in Settings → About Phone → MIUI version (tap 7 times) and execute the command: adb shell sm set-force-adoptable true After the reboot, try formatting again.
⚠️ Attention: Teams ADB They can cause failures if entered incorrectly. MIUI 13 and later, this method is not officially supported and may cause errors when installing updates.
How to return the card to its original state?
Speed of operation: comparison of internal and combined memory
The combined memory card will always be slower than the built-in eMMC. Below are the test data on the Redmi 9 with a 128GB SanDisk Ultra A2 card:
| Type of memory | Reading speed (MB/s) | Recording speed (MB/s) | Delay (MS) |
|---|---|---|---|
| Internal (eMMC 5.1) | 250–280 | 120–150 | 0.1–0.3 |
| Combined (microSD U3) | 80–95 | 30–50 | 1.2–2.0 |
| Portable (microSD exFAT) | 90–100 | 40–60 | 0.8–1.5 |
And you can see that combined memory loses almost 3 times the write speed, which is critical for:
- 🎮 Games (such as Genshin Impact or Call of Duty Mobile) will slow down).
- 📷 Camera applications when shooting in 4K.
- 🎵 Music players with caching (e.g. Spotify).
For everyday tasks (messaging, social networks, documents), the difference is small. If you use your phone for games or videos, you should buy a model with a large amount of internal memory (for example, Redmi 9 128 GB).
Alternatives to joining together: when it is better not to risk
If you are concerned about the risks (data loss, slow work), consider alternatives:
- 🔄 Manual Application Transfer: C Settings → Select the program and click Transfer to SD-Card (not working for all applications).
- ☁️ Cloud storage: Google Drive, Mi Cloud or Yandex Disk with autosynchronization of photos and videos.
- 📁 File Manager: Manually move heavy files (such as downloads or cache) to the map via Explorer or Solid Explorer.
- 🔧 Memory optimization: Remove the cache (Settings) → Memory. → Clear cache) and unnecessary applications.
To automatically transfer files, set up the default storage in the camera and messenger settings. For example, on WhatsApp, this is done in Settings → Storage and Data → Media Saving.
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Memory card integration is only justified if you critically lack the space to install applications. In all other cases, it is better to use alternative methods.
Frequent mistakes and their solutions
Redmi 9 users often face the following problems:
- The phone doesn't see the card when you combine it. So, reboot the device. If it doesn't, pull the card out, paste it back in, and wait for the suggestion to format it again.
- Applications are not installed on the map. Solution: check if the application supports portability (in Google Play this is indicated in the "Permissions" section).
- After the MIUI update, the card crashed. Solution: update the firmware to the latest version through Settings → System Update. If the problem persists, reset the settings (the data on the phone will save, but the map will have to be formatted again).
⚠️ Warning: If the phone starts to warm up or run out quickly after the combination, check the card for authenticity. Fake microSDs (especially low-priced branded ones) can cause a memory controller to malfunction.