Issues creating multiple LittleFS file systems in external flash

RE: Issues creating multiple LittleFS file systems in external flash

Monkeytronics — Thu, 02 Apr 2026 00:19:10 GMT

You must have the patience of a saint to have figured that out. Well done and thanks for sharing the solution in such a digestible format.

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Mon, 30 Mar 2026 16:22:07 GMT

I did get a working solution but then got sidetracked onto a higher priority issue and am just getting back to this.

Dejan's reply above was almost correct. When he patched the SDK, he named the new partitions 'lfs_part_X' where X is a digit starting at 0. The entries in the pm_static.yml need to start at 0(not 1 as given in his example code. After making that change, I could mount two different partitions.

My final .overlay file has these sections in it:

    /* External flash definition. */
    ext_flash: w25q128jv@0  {
		compatible = "jedec,spi-nor";
		reg = <0>;
		spi-max-frequency = <100000000>;    // HW max is 133 MHz
		jedec-id = [ef 70 18];
		size = <0x8000000>;                 // Memory's size in bits (128 Mbits)
        partitions {
            compatible = "fixed-partitions";
            #address-cells = <1>;
            #size-cells = <1>;
            app_fs: partition@0 {
                status = "okay";
                // label is only used to document entry in pm_static.yml
                label = "lfs_part_0";
                reg = <0x0 0x500000>;       // Partition size in bytes (5 MBytes)
            };

            log_fs: partition@500000 {
                status = "okay";
                // label is only used to document entry in pm_static.yml
                label = "lfs_part_1";
                reg = <0x500000 0x900000>;  // Partition size in bytes (9 MBytes)
            };
        };
	};

    /* Configuration for littleFS to be mounted before boot */
    fstab {
        compatible = "zephyr,fstab";
        fs: fs{
            compatible = "zephyr,fstab,littlefs";
            mount-point = "/fs";
            partition = <&app_fs>;
            automount;
            read-size = <16>;
            prog-size = <16>;
            cache-size = <4096>;
            lookahead-size = <32>;
            block-cycles = <512>;
        };

        log: log{
            compatible = "zephyr,fstab,littlefs";
            mount-point = "/data";
            partition = <&log_fs>;
            automount;
            read-size = <16>;
            prog-size = <16>;
            cache-size = <4096>;
            lookahead-size = <64>;
            block-cycles = <128>;
        };
    };

My pm_static.yml contains:

# The external partitions need to follow the naming pattern defined in
# zephyr/subsys/fs/littlefs_fs.c of the NCS SDK that is used to build the
# application.  This defaults to 'littlefs_storage' in the standard release
# which only allows a single instance of a LittleFS filesystem to be defined.
#
# Our fork of the SDK has been patched to change this to 'lfs_part_?' which
# allows multiple partitions to be defined.

lfs_part_0:
  address: 0x0
  end_address: 0x500000
  region: external_flash
  size: 0x500000

lfs_part_1:
  address: 0x500000
  end_address: 0x1000000
  region: external_flash
  size: 0xb00000

I think I also had an issue with the system still wanting to create a 'littlefs_storage' partition and ended up setting this in my prj.conf to stop that:

# Set the size of the 'littlefs_storage' partition to zero, so that it doesn't get created
CONFIG_PM_PARTITION_SIZE_LITTLEFS=0x0

I plan on updating my example code repo to show a working example but haven't had the time to do that yet.

Hopefully this will get you started on the right path.

Jeff

RE: Issues creating multiple LittleFS file systems in external flash

Monkeytronics — Sun, 29 Mar 2026 08:42:34 GMT

Did you ever solve this or did Jeff give up on the grounds that this is so spectacularly complicated? Here's the thing. I'd also like to put little fs onto external flash after the secondary app partition. It sounds like you don't have a working recipe and are cobbling together a process where you create a starting point that generates a partition.yml. Then you hand modify the partition.yml and save it as static_pm.yml. Do I have that right?

RE: Issues creating multiple LittleFS file systems in external flash

dejans — Tue, 20 Jan 2026 17:47:22 GMT

Hi Jeff,

[quote user="Jeff Cooper"]Now everything (including block-cycles) has changed to match the device tree fstab values except for the size of the partition. [/quote]

In NCS v3.2.1 all sizes should match fstab values. The partition sizes are expected to be taken from partition manager static configuration.

You can try out configuration files shown below (2 lfs_part partitions of 64 KB and 1 MB are made in external flash as can be seen from partition manager report)
pm_static.yml

app:
  address: 0x0
  end_address: 0x100000
  region: flash_primary
  size: 0x100000
external_flash:
  address: 0x6000
  end_address: 0x800000
  region: external_flash
  size: 0x7fa000
littlefs_storage:
  address: 0x0
  device: DT_CHOSEN(nordic_pm_ext_flash)
  end_address: 0x6000
  placement:
    before:
    - tfm_storage
    - end
  region: external_flash
  size: 0x6000
lfs_part_1:
  address: 0x6000
  device: DT_CHOSEN(nordic_pm_ext_flash)
  end_address: 0x16000
  placement:
    before:
    - tfm_storage
    - end
  region: external_flash
  size: 0x10000
lfs_part_2:
  address: 0x16000
  device: DT_CHOSEN(nordic_pm_ext_flash)
  end_address: 0x116000
  placement:
    before:
    - tfm_storage
    - end
  region: external_flash
  size: 0x100000
sram_primary:
  address: 0x20000000
  end_address: 0x20040000
  region: sram_primary
  size: 0x40000

nrf52840dk_nrf52840.overlay

/*
 * Copyright (c) 2019 Peter Bigot Consulting, LLC
 *
 * SPDX-License-Identifier: Apache-2.0
 */


 / {
	chosen {
		nordic,pm-ext-flash = &mx25r64;
	};
};


/delete-node/ &storage_partition;

/ {
	fstab {
		compatible = "zephyr,fstab";
		app_fs: app_fs {
			compatible = "zephyr,fstab,littlefs";
			mount-point = "/fs";
			partition = <&app_fs_part>;
			automount;
			read-size = <16>;
			prog-size = <16>;
			cache-size = <64>;
			lookahead-size = <32>;
			block-cycles = <512>;
		};

		log_fs: log_fs{
            compatible = "zephyr,fstab,littlefs";
            mount-point = "/log";
            partition = <&log_fs_part>;
            automount;
            read-size = <16>;
            prog-size = <16>;
            cache-size = <4096>;
            lookahead-size = <64>;
            block-cycles = <128>;
        };

		log_fs_2: log_fs_2{
            compatible = "zephyr,fstab,littlefs";
            mount-point = "/log_2";
            partition = <&log_fs_part_2>;
            automount;
            read-size = <16>;
            prog-size = <16>;
            cache-size = <4096>;
            lookahead-size = <64>;
            block-cycles = <128>;
        };
	};
};

&mx25r64 {
	partitions {
		compatible = "fixed-partitions";
		#address-cells = <1>;
		#size-cells = <1>;

		app_fs_part: partition@0 {
			label = "storage";
			reg = <0x00000000 0x00010000>;
		};

		log_fs_part: partition@10000 {
			label = "logs";
			reg = <0x00010000 0x00050000>;
		};

		log_fs_part_2: partition@50000 {
			label = "logs_2";
			reg = <0x00050000 0x00090000>;
		};

	};
};

Partition manager report (west build -t partition_manger_report)

external_flash (0x800000 - 8192kB): 
+--------------------------------------------+
| 0x0: littlefs_storage (0x6000 - 24kB)      |
| 0x6000: external_flash (0x7fa000 - 8168kB) |
| 0x6000: lfs_part_1 (0x10000 - 64kB)        |
| 0x16000: lfs_part_2 (0x100000 - 1024kB)    |
+--------------------------------------------+

  flash_primary (0x100000 - 1024kB): 
+------------------------------+
| 0x0: app (0x100000 - 1024kB) |
+------------------------------+

  sram_primary (0x40000 - 256kB): 
+--------------------------------------------+
| 0x20000000: sram_primary (0x40000 - 256kB) |
+--------------------------------------------+

[quote user="Jeff Cooper"]If I need to create a 'pm_static.yml' to define my partitions for the partition manager, how does that relate to the device tree fstab entries?[/quote]

When partition manager is used, entries in the devicetree are not used.

For having multiple littlefs partitions when using partition manager, following SDK changes are also needed:

diff --git a/subsys/fs/littlefs_fs.c b/subsys/fs/littlefs_fs.c
index 5abbf95f949..0e155437fc5 100644
--- a/subsys/fs/littlefs_fs.c
+++ b/subsys/fs/littlefs_fs.c
@@ -1105,8 +1105,8 @@ struct fs_mount_t FS_FSTAB_ENTRY(DT_DRV_INST(inst)) = { \
        .fs_data = &fs_data_##inst, \
        .storage_dev = (void *) \
                COND_CODE_1(USE_PARTITION_MANAGER, \
-                           (COND_CODE_1(FIXED_PARTITION_EXISTS(littlefs_storage), \
-                                        (FIXED_PARTITION_ID(littlefs_storage)), \
+                           (COND_CODE_1(FIXED_PARTITION_EXISTS(lfs_part##inst), \
+                                        (FIXED_PARTITION_ID(lfs_part##inst)), \
                                         (FIXED_PARTITION_ID(storage)))), \
                            (DT_FIXED_PARTITION_ID(FS_PARTITION(inst)))), \
        .flags = FSTAB_ENTRY_DT_MOUNT_FLAGS(DT_DRV_INST(inst)), \

Best regards,
Dejan

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Fri, 16 Jan 2026 02:26:49 GMT

Hi Dejan,

All of the images that I'm running below were built with sysbuild.

The values I changed were in the fstab entry of the device tree. I made a change to them to see if the image was using those values from the device tree or was getting them from somewhere else.

When I boot an image from the nordic_suggestions.3.2.1 branch built with NCS 2.7.0:

I: LittleFS version 2.8, disk version 2.1
I: FS at mx25r6435f@0:0x0 is 16 0x1000-byte blocks with 512 cycle
I: sizes: rd 16 ; pr 16 ; ca 64 ; la 32
I: Automount /lfs1 succeeded
*** Booting nRF Connect SDK v2.7.0-5cb85570ca43 ***

16 0x1000-byte: second value of reg entry for the partition (0x00010000)

block-cycles: 512 cycle

rd (read-size): 16

pr (prog-size): 16

ca (cache-size): 64

la (lookahead-size): 32

If I modify those values as shown below and rebuild with NCS 2.7.0.:

I get the following output:

I: LittleFS version 2.8, disk version 2.1
I: FS at mx25r6435f@0:0x0 is 32 0x1000-byte blocks with 512 cycle
I: sizes: rd 4 ; pr 8 ; ca 16 ; la 64
I: Automount /lfs1 succeeded
*** Booting nRF Connect SDK v2.7.0-5cb85570ca43 ***

So we can see that all of the values were updated in the output except for the block-cycles, that still stayed at 512 even though I tried to set it to 256.

The size of the file system also changed from 16 0x1000 byte blocks to 32 blocks following the change of the value of the reg entry in the partition table for the 'lfs1_part' entry.

Now, if I build with NCS 2.8.0:

I: LittleFS version 2.9, disk version 2.1
I: FS at mx25r6435f@0:0x0 is 6 0x1000-byte blocks with 512 cycle
I: sizes: rd 4 ; pr 8 ; ca 16 ; la 64
I: Automount /lfs1 succeeded
*** Booting nRF Connect SDK v2.8.0-a2386bfc8401 ***

The changed values in the fstab entry are still changed in this output (except for the block-cycles) however, the file system size is now 6 0x1000 byte blocks and not the 32 0x1000 byte blocks specified in the 'lfs1_part' entry of the device tree.

If I build with NCS 3.2.1:

I: LittleFS version 2.11, disk version 2.1
I: FS at mx25r6435f@0:0x0 is 6 0x1000-byte blocks with 256 cycle
I: partition sizes: rd 4 ; pr 8 ; ca 16 ; la 64
I: Automount /lfs1 succeeded
*** Booting nRF Connect SDK v3.2.1-d8887f6f32df ***

Now everything (including block-cycles) has changed to match the device tree fstab values except for the size of the partition. I assume that the block-cycle not changing was a bug that was fixed at some point.

What I'm not understanding is how to configure the partitions and fstab entries when using a NCS that is 2.8.0 or newer.

If I remove the 'partition' entry in fstab, I get the following error when trying to build in NCS 3.2.1:

-- Found devicetree overlay: /home/jeffc/projects/test/littlefs/boards/nrf52840dk_nrf52840.overlay
devicetree error: 'partition' is marked as required in 'properties:' in /home/jeffc/ncs/v3.2.1/zephyr/dts/bindings/fs/zephyr,fstab,littlefs.yaml, but does not appear in <Node /fstab/lfs1 in /home/jeffc/projects/test/littlefs/boards/nrf52840dk_nrf52840.overlay:17>

So, it appears that I need a partition entry in fstab to point at something in the devicetree, but the information in it isn't being used.

If I need to create a 'pm_static.yml' to define my partitions for the partition manager, how does that relate to the device tree fstab entries?

thanks,

Jeff

RE: Issues creating multiple LittleFS file systems in external flash

dejans — Thu, 15 Jan 2026 23:00:22 GMT

Hi Jeff,

I used your nordic_suggestions.3.2.1 branch for testing and got this result

I: littlefs partition at /fs
I: LittleFS version 2.11, disk version 2.1
D: FS area 1 at 0x0 for 24576 bytes
I: FS at mx25r6435f@0:0x0 is 6 0x1000-byte blocks with 512 cycle
I: partition sizes: rd 16 ; pr 16 ; ca 64 ; la 32
E: WEST_TOPDIR/modules/fs/littlefs/lfs.c:1386: Corrupted dir pair at {0x0, 0x1}
W: can't mount (LFS -84); formatting
I: /fs mounted
D: fs mounted at /fs
I: Automount /fs succeeded
I: littlefs partition at /log
I: LittleFS version 2.11, disk version 2.1
D: FS area 1 at 0x0 for 24576 bytes
I: FS at mx25r6435f@0:0x0 is 6 0x1000-byte blocks with 128 cycle
I: partition sizes: rd 16 ; pr 16 ; ca 4096 ; la 64
D: fs mounted at /log
I: Automount /log succeeded
*** Booting nRF Connect SDK v3.2.1-d8887f6f32df ***
*** Using Zephyr OS v4.2.99-ec78104f1569 ***
Sample program to r/w files on littlefs
Area 1 at 0x0 on mx25r6435f@0 for 24576 bytes
/fs was automounted
/fs: bsize = 16 ; frsize = 4096 ; blocks = 6 ; bfree = 4

Listing dir / ...
[DIR ] fs
[DIR ] log

Listing dir /fs ...

Listing dir /log ...

/fs/boot_count read count:0 (bytes: 0)
/fs/boot_count write new boot count 1: [wr:1]
I: /fs unmounted
D: fs unmounted from /fs
/fs unmount: 0

Here is the output of "west build -t partition_manager_report":

 external_flash (0x800000 - 8192kB):
+--------------------------------------------+
| 0x0: littlefs_storage (0x6000 - 24kB)      |
| 0x6000: external_flash (0x7fa000 - 8168kB) |
+--------------------------------------------+

  flash_primary (0x100000 - 1024kB):
+------------------------------+
| 0x0: app (0x100000 - 1024kB) |
+------------------------------+

  sram_primary (0x40000 - 256kB):
+--------------------------------------------+
| 0x20000000: sram_primary (0x40000 - 256kB) |
+--------------------------------------------+

Do you get the same result?

[quote user="Jeff Cooper"]

This version does appear to use the file system values for read-size, prog-size, etc that are defined in the fstab in the device tree. I can make changes to those values and see the change in the log output when the file system is mounted.

It doesn't appear to use the partition size defined in the device tree.

[/quote]

Can you point to relevant values that you tried to change and how?
Can you elaborate on " I can make changes to those values and see the change in the log output when the file system is mounted."?

[quote user="Jeff Cooper"]It doesn't appear to use the partition size defined in the device tree.[/quote]

Which partition size do you refer to? What is your expectation regarding partition size?

Best regards,
Dejan

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Wed, 14 Jan 2026 15:56:32 GMT

Hi Dejan,

No, the littlefs sample does not work as expected.

I started out with trying the example as-is building with sysbuild and NCS 3.2.1. That built but when flashed to a nRF52840DK it created a 24 kiB LittleFS file system on the internal flash.

I believe that was due to the name of the overlay file: boards/nrf52840dk_nrf52840_qspi.overlay.

Next, I renamed that overlay file to boards/nrf52840dk_nrf52840.overlay which was found by the build. When I flashed that version, it still created a 24 kiB LittleFS file system on the internal flash.

I: littlefs partition at /lfs1
I: LittleFS version 2.11, disk version 2.1
I: FS at flash-controller@4001e000:0xfa000 is 6 0x1000-byte blocks with 512 cycle
I: partition sizes: rd 16 ; pr 16 ; ca 64 ; la 32
E: WEST_TOPDIR/modules/fs/littlefs/lfs.c:1386: Corrupted dir pair at {0x0, 0x1}
W: can't mount (LFS -84); formatting
I: /lfs1 mounted
I: Automount /lfs1 succeeded
*** Booting nRF Connect SDK v3.2.1-d8887f6f32df ***
*** Using Zephyr OS v4.2.99-ec78104f1569 ***
Sample program to r/w files on littlefs
Area 1 at 0xfa000 on flash-controller@4001e000 for 24576 bytes
/lfs1 automounted
/lfs1: bsize = 16 ; frsize = 4096 ; blocks = 6 ; bfree = 4

I believe that was due to me not having your suggested changes implemented:

Add CONFIG_PM_PARTITION_REGION_LITTLEFS_EXTERNAL=y to prj.conf
Add a chosen section to the device tree overlay.

Next, I added those changes to their respective files and rebuilt and flashed. That did create a LittleFS file system on the external flash but it was not the size defined in the devicetree. It was still 24 kiB. The partition defined in the device tree is 64 kiB.

I: littlefs partition at /lfs1
I: LittleFS version 2.11, disk version 2.1
I: FS at mx25r6435f@0:0x0 is 6 0x1000-byte blocks with 512 cycle
I: partition sizes: rd 16 ; pr 16 ; ca 64 ; la 32
I: Automount /lfs1 succeeded
*** Booting nRF Connect SDK v3.2.1-d8887f6f32df ***
*** Using Zephyr OS v4.2.99-ec78104f1569 ***
Sample program to r/w files on littlefs
Area 1 at 0x0 on mx25r6435f@0 for 24576 bytes
/lfs1 automounted
/lfs1: bsize = 16 ; frsize = 4096 ; blocks = 6 ; bfree = 3

It doesn't appear to use the partition size defined in the device tree.

I've added a branch to my repo that has these latest changes in it:

https://github.com/repoocaj/littlefs/tree/nodic_suggestions.3.2.1

If you run that branch on a nRF52840DK do you get the same results?

thanks,

Jeff

RE: Issues creating multiple LittleFS file systems in external flash

dejans — Wed, 14 Jan 2026 09:49:29 GMT

Hi Jeff,

If you start from unmodified littlefs sample linked previously, does having only one littlefs file system on external flash work for you in NCS v3.2.1 (sysbuild enabled)?

Best regards,
Dejan

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Tue, 13 Jan 2026 15:37:40 GMT

The code in my example repo is based on the Zephyr littlefs example.

I've added code to demonstrate the issue I'm having with multiple LittleFS file systems on external flash and to remove some unnecessary board files and the pattern test.

Can you clone this branch:

https://github.com/repoocaj/littlefs/tree/mcuboot.3.2.1

And take a look at the example? This branch is meant to be built with NCS 3.2.1.

I've had the changes you suggested above in the example since I asked my original question.

I have a 'pm_static.yml' defined for my two LittleFS partitions on the external flash, but I don't know how to reference them in my device tree fstab entry.

thanks,

Jeff

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Tue, 13 Jan 2026 15:26:07 GMT

I'm not sure how to build a multi image without sysbuild.

I checked out my 'mcuboot-3.2.1' branch from my example repo and created two build configurations in VS Code, one with sysbuild and one without.

That created an applications entry in VS Code that looks like:

So it doesn't look like VS Code created multi images without using sysbuild.

If I flash the 'build-no-sysbuild' image, it works in that it correctly mounts the LittleFS partitions on the external flash, but it didn't use MCUboot.

If I flash the 'build-sysbuild' images, it uses MCUboot but doesn't mount the partitions from external flash.

Jeff

RE: Issues creating multiple LittleFS file systems in external flash

dejans — Tue, 13 Jan 2026 14:57:29 GMT

Hi Jeff,

For reference, you can look at Zephyr littlefs sample.
You need to ensure that you include CONFIG_PM_PARTITION_REGION_LITTLEFS_EXTERNAL=y in your prj.conf and the following app.overlay file:

/ {
	chosen {
		nordic,pm-ext-flash = &mx25r64;
	};
};

Best regards,
Dejan

RE: Issues creating multiple LittleFS file systems in external flash

dejans — Tue, 13 Jan 2026 12:41:14 GMT

Hi Jeff,

Do you have multi image builds in both cases, with and without sysbuild?

Best regards,
Dejan

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Mon, 12 Jan 2026 16:44:44 GMT

Dejan,

Can you provide any assistance in defining a partition layout that will be accepted by partition manager and sysbuild that would allow a pair of LittleFS file systems to exist in the external flash on a nRF52840DK?

The link about the partition manager activation that you gave states that:

When you build a multi-image application using the Partition Manager, the devicetree source flash partitions are ignored.

I'm taking that to mean that I don't define my external partitions with an entry in the device tree like:

&mx25r64 {
	partitions {
		compatible = "fixed-partitions";
		#address-cells = <1>;
		#size-cells = <1>;

		app_fs_part: partition@0 {
			label = "storage";
			reg = <0x00000000 0x00010000>;
		};

		log_fs_part: partition@10000 {
			label = "logs";
			reg = <0x00010000 0x00050000>;
		};
	};
};

However, my fstab entry in my device tree looks like:

	fstab {
		compatible = "zephyr,fstab";
		app_fs: app_fs {
			compatible = "zephyr,fstab,littlefs";
			mount-point = "/fs";
			partition = <&app_fs_part>;
			automount;
			read-size = <16>;
			prog-size = <16>;
			cache-size = <64>;
			lookahead-size = <32>;
			block-cycles = <512>;
		};

		log_fs: log_fs{
            compatible = "zephyr,fstab,littlefs";
            mount-point = "/log";
            partition = <&log_fs_part>;
            automount;
            read-size = <16>;
            prog-size = <16>;
            cache-size = <4096>;
            lookahead-size = <64>;
            block-cycles = <128>;
        };
	};

Where the partition entry (e.g. 'partition = <&app_fs_part>;') references the entries in the device tree partition table.

How do I create references to partitions that are defined by the partition manager?

thanks,

Jeff

RE: Issues creating multiple LittleFS file systems in external flash

dejans — Mon, 12 Jan 2026 10:49:33 GMT

Hi,

[quote user="Jeff Cooper"]Do you know why using sysbuild would be causing this issue?[/quote]

Support for partition manager for an image was moved to sysbuild and partition manager is activated for all sysbuild builds.

Best regards,
Dejan

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Fri, 09 Jan 2026 15:43:17 GMT

If I build the single file system version without sysbuild in both NCS 2.8.0 and 3.2.1, the LittleFS partition is mounted correctly from the external flash.

I also tried the dual file system branch and that works as well.

D: fs register 1: 0
I: littlefs partition at /fs
I: LittleFS version 2.9, disk version 2.1
D: FS area 0 at 0x0 for 65536 bytes
I: FS at mx25r6435f@0:0x0 is 16 0x1000-byte blocks with 512 cycle
I: sizes: rd 4 ; pr 8 ; ca 16 ; la 16
D: fs mounted at /fs
I: Automount /fs succeeded
*** Booting nRF Connect SDK v2.8.0-a2386bfc8401 ***
*** Using Zephyr OS v3.7.99-0bc3393fb112 ***
Sample program to r/w files on littlefs
Area 0 at 0x0 on mx25r6435f@0 for 65536 bytes
/fs was automounted
/fs: bsize = 8 ; frsize = 4096 ; blocks = 16 ; bfree = 14

Listing dir / ...
[DIR ] fs

Listing dir /fs ...
[FILE] boot_count (size = 1)
/fs/boot_count read count:7 (bytes: 1)
/fs/boot_count write new boot count 8: [wr:1]
I: /fs unmounted
D: fs unmounted from /fs
/fs unmount: 0

Do you know why using sysbuild would be causing this issue?

I haven't testing enabling MCUboot and building without sysbuild yet.

RE: Issues creating multiple LittleFS file systems in external flash

dejans — Fri, 09 Jan 2026 10:25:13 GMT

Hi Jeff,

What is the result when you build single file system without sysbuild (in NCS v2.8.0 and v3.2.1)?
You can choose the option "No Sysbuild" for Build Configuration in VS Code or use --no-sysbuild flag when building using west.

Best regards,
Dejan

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Thu, 08 Jan 2026 20:02:04 GMT

Dejan,

I forgot to add that I tried changing more of the values in the fstab (read-size, prog-size, cache-size, lookahead-size and block-cycles). Those are picked up and used when mounting the file system.

It just seems to be ignoring what the partition value is set to or it's being overwritten somehow.

The `partitions.yml` generated by the 3.2.1 build looks like:

app:
  address: 0x0
  end_address: 0xfa000
  region: flash_primary
  size: 0xfa000
littlefs_storage:
  address: 0xfa000
  end_address: 0x100000
  placement:
    before:
    - end
  region: flash_primary
  size: 0x6000
sram_primary:
  address: 0x20000000
  end_address: 0x20040000
  region: sram_primary
  size: 0x40000

So it's not doing anything with the external flash.

Jeff

RE: Issues creating multiple LittleFS file systems in external flash

Jeff — Thu, 08 Jan 2026 19:46:15 GMT

He Dejan,

Thanks for looking into this.

When I've been generating my build configurations in VS Code, I've just been selecting 'Build System default' as the system build option. Following your suggestion, I selected the 'sysbuild' option and removed one of the file systems from use in the code.

I also removed the previous configuration (from within VS Code) and recreated it for each build to make sure that there wasn't any leftover stuff influencing the build.

I built and tested with both 2.8.0 and 3.2.1 and the results are essentially the same other than the changes of the OS version and LittleFS versions. Both versions didn't mount a LittleFS on the external flash and didn't use the size defined in fstab and partitions defined in the overlay file.

I did verify in the build output that the build located my overlay file:

-- Found devicetree overlay: /home/jeffc/projects/test/littlefs/boards/nrf52840dk_nrf52840.overlay

Here's the output of the 3.2.1 build running on a nRF52840DK:

D: fs register 1: 0
I: littlefs partition at /fs
I: LittleFS version 2.11, disk version 2.1
D: FS area 1 at 0xfa000 for 24576 bytes
I: FS at flash-controller@4001e000:0xfa000 is 6 0x1000-byte blocks with 512 cycle
I: partition sizes: rd 16 ; pr 16 ; ca 64 ; la 32
D: fs mounted at /fs
I: Automount /fs succeeded
*** Booting nRF Connect SDK v3.2.1-d8887f6f32df ***
*** Using Zephyr OS v4.2.99-ec78104f1569 ***
Sample program to r/w files on littlefs
Area 1 at 0xfa000 on flash-controller@4001e000 for 24576 bytes
/fs was automounted
/fs: bsize = 16 ; frsize = 4096 ; blocks = 6 ; bfree = 4

Listing dir / ...
[DIR ] fs

Listing dir /fs ...
[FILE] boot_count (size = 1)
/fs/boot_count read count:2 (bytes: 1)
/fs/boot_count write new boot count 3: [wr:1]
I: /fs unmounted
D: fs unmounted from /fs
/fs unmount: 0

I've pushed my changes for the single file system test to a branch, single_fs, in my github repo:

https://github.com/repoocaj/littlefs/tree/single_fs

thanks,

Jeff

RE: Issues creating multiple LittleFS file systems in external flash

dejans — Thu, 08 Jan 2026 17:36:39 GMT

Hi Jeff,

[quote user=""] if I build the same project with NCS 2.8.0 and flash it to the same board, it doesn't work. It's now using the internal flash and both file systems are using the same area of flash and are of the same size[/quote]

What happens if you use only one file system (instead of two) in NCS v2.8.0 (and NCS v3.2.1)?

Have you built your project in NCS v2.8.0 and NCS v3.2.1 using sysbuild?

Best regards,
Dejan