Define specific compiler version for module building

[M-Stenzel]

Question

I built the Linux kernel with the Advanced Toolchain

https://www.ibm.com/support/pages/advance-toolchain-linux-power

residing in the /opt directory

Compiling kernel modules fail:

cd "/lib/modules/"6.12.0-160000.28-lucy"/build" && make M=/tmp/open-cas-linux-25.12.2/modules modules
make[2]: Entering directory '/usr/src/linux-6.12.0-160000.28'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: gcc-13 (GCC) 15.1.1 20250502 (Advance-Toolchain 19.0-0) [066115a7a44a]
  You are using:           gcc-13 (SUSE Linux) 13.4.0
  CC [M]  /tmp/open-cas-linux-25.12.2/modules/cas_cache/classifier.o
In file included from /tmp/open-cas-linux-25.12.2/modules/cas_cache/cas_cache.h:13,
                 from /tmp/open-cas-linux-25.12.2/modules/cas_cache/classifier.c:7:
/tmp/open-cas-linux-25.12.2/modules/include/cas_ioctl_codes.h:182:26: error: ‘OCF_CORE_MAX’ undeclared here (not in a function); did you mean ‘OCF_ERR_MAX’?
  182 |         uint16_t core_id[OCF_CORE_MAX];
      |                          ^~~~~~~~~~~~
      |                          OCF_ERR_MAX
make[5]: *** [scripts/Makefile.build:229: /tmp/open-cas-linux-25.12.2/modules/cas_cache/classifier.o] Error 1

My kernel .config file includes this:

CONFIG_CC_VERSION_TEXT="gcc-13 (GCC) 15.1.1 20250502 (Advance-Toolchain 19.0-0) [066115a7a44a]"

In the open-cas-linux software files there are many references to gcc.
I tried to change entries in different files, no success....

How can I define the C compiler in the software? Running "./configure" does not allow me to change the compiler version, the variable "CC" gets ignored.

I checked with different open-cas versions, and the error seems related to the kernel version,
is it too new?

Motivation

The kernel runs faster with this compiler

Your Environment

• OpenCAS version: 25.12.2
• Operating System: openSUSE 16.0, ppc64le
• Kernel version: 6.12.0 (from rpm packages)

[robertbaldyga]

Hi @M-Stenzel ! Whoa, OpenCAS on ppc is not something you see everyday!

The compilation error looks like a missing submodule update.

The compiler, well, we never needed to use any other compiler than gcc, so for now it's just hardcoded.
Luckily it's just a handful of places, so as a quick fix I'd just go for simple substitution:

root@bench1:~/open-cas-linux# git grep gcc
casadm/csvparse.c: * gcc -ggdb csvparse.c -I../common -D__CSV_SAMPLE__ -ocsvsample
configure:check_util gcc
configure.d/Makefile:   gcc -c -xc ${1} -o /dev/null - 2>/dev/null; \
modules/config.mk:      gcc -c -xc ${1} -o /dev/null - 2>/dev/null; \
modules/config.mk:      gcc -c -xc -o /dev/null - 2>/dev/null; \
tools/pckgen.d/rpm/CAS_NAME.spec:BuildRequires: gcc

If you feel like sending a patch that does the actual parametrization in Makefiles, I'd be happy to accept it. If not, I'll try to find some time for it before the next release.

[M-Stenzel]

Hi @M-Stenzel ! Whoa, OpenCAS on ppc is not something you see everyday!

The compilation error looks like a missing submodule update.

The compiler, well, we never needed to use any other compiler than gcc, so for now it's just hardcoded. Luckily it's just a handful of places, so as a quick fix I'd just go for simple substitution:

root@bench1:~/open-cas-linux# git grep gcc
casadm/csvparse.c: * gcc -ggdb csvparse.c -I../common -D__CSV_SAMPLE__ -ocsvsample
configure:check_util gcc
configure.d/Makefile:   gcc -c -xc ${1} -o /dev/null - 2>/dev/null; \
modules/config.mk:      gcc -c -xc ${1} -o /dev/null - 2>/dev/null; \
modules/config.mk:      gcc -c -xc -o /dev/null - 2>/dev/null; \
tools/pckgen.d/rpm/CAS_NAME.spec:BuildRequires: gcc

If you feel like sending a patch that does the actual parametrization in Makefiles, I'd be happy to accept it. If not, I'll try to find some time for it before the next release.

Oh, thank you for the fast response.
Well, I did check my kernel source directory and the open-cas directory, there was no entry regarding the "system" gcc.
Moreover I tried to trick the build system with replacing the "system" gcc with the Advance Toolchain gcc. This did not work either. I checked environment variables, paths, /proc/version, uname, everything - crazy, all did not work.

Building "casadm" and "utils" works well.

[M-Stenzel]

O. K. This is an update to the topic.
After booting the SUSE provided default kernel (6.12.0), and using the default gcc (13.4.0) I still receive an error like this:

cd "/lib/modules/"6.12.0-160000.27-default"/build" && make M=/scratch/open-cas-linux-26.03.1.1031.release/modules modules
make[2]: Entering directory '/usr/src/linux-6.12.0-160000.27-obj/ppc64le/default'
make --no-print-directory -C /usr/src/linux-6.12.0-160000.27-obj/ppc64le/default \
-f /usr/src/linux-6.12.0-160000.27/Makefile modules
make -f /usr/src/linux-6.12.0-160000.27/scripts/Makefile.build obj=/scratch/open-cas-linux-26.03.1.1031.release/modules need-builtin=1 need-modorder=1 
make -f /usr/src/linux-6.12.0-160000.27/scripts/Makefile.build obj=/scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache \
need-builtin=1 \
need-modorder=1 \

# CC [M]  /scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache/service_ui_ioctl.o
  gcc-13 -Wp,-MMD,/scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache/.service_ui_ioctl.o.d -nostdinc -I/usr/src/linux-6.12.0-160000.27/arch/powerpc/include -I./arch/powerpc/include/generated -I/usr/src/linux-6.12.0-160000.27/include -I./include -I/usr/src/linux-6.12.0-160000.27/arch/powerpc/include/uapi -I./arch/powerpc/include/generated/uapi -I/usr/src/linux-6.12.0-160000.27/include/uapi -I./include/generated/uapi -include /usr/src/linux-6.12.0-160000.27/include/linux/compiler-version.h -include /usr/src/linux-6.12.0-160000.27/include/linux/kconfig.h -include /usr/src/linux-6.12.0-160000.27/include/linux/compiler_types.h -D__KERNEL__ -DCC_USING_PATCHABLE_FUNCTION_ENTRY -I /usr/src/linux-6.12.0-160000.27/arch/powerpc -DHAVE_AS_ATHIGH=1 -fmacro-prefix-map=/usr/src/linux-6.12.0-160000.27/= -std=gnu11 -fshort-wchar -funsigned-char -fno-common -fno-PIE -fno-strict-aliasing -mlittle-endian -m64 -msoft-float -mtraceback=no -mabi=elfv2 -mcmodel=medium -mno-pointers-to-nested-functions -mlong-double-128 -mcpu=power9 -mno-prefixed -mno-pcrel -mno-altivec -mno-vsx -mno-mma -fno-asynchronous-unwind-tables -mno-string -mno-strict-align -mlittle-endian -mstack-protector-guard=tls -mstack-protector-guard-reg=r13 -fno-delete-null-pointer-checks -O2 -fno-allow-store-data-races -fstack-protector-strong -fno-stack-clash-protection -fpatchable-function-entry=1 -flive-patching=inline-clone -fmin-function-alignment=4 -fstrict-flex-arrays=3 -fno-strict-overflow -fno-stack-check -fconserve-stack -Wall -Wundef -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Werror=strict-prototypes -Wno-format-security -Wno-trigraphs -Wno-frame-address -Wno-address-of-packed-member -Wmissing-declarations -Wmissing-prototypes -Wframe-larger-than=2048 -Wno-main -Wno-dangling-pointer -Wvla -Wno-pointer-sign -Wcast-function-type -Wno-stringop-overflow -Wno-array-bounds -Wno-alloc-size-larger-than -Wimplicit-fallthrough=5 -Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init -Wenum-conversion -Wextra -Wunused -Wno-unused-but-set-variable -Wno-unused-const-variable -Wno-packed-not-aligned -Wno-format-overflow -Wno-format-truncation -Wno-stringop-truncation -Wno-override-init -Wno-missing-field-initializers -Wno-type-limits -Wno-shift-negative-value -Wno-maybe-uninitialized -Wno-sign-compare -Wno-unused-parameter -g -gdwarf-5 -mstack-protector-guard-offset=3192 -DCAS_VERSION_MAIN=26 -DCAS_VERSION_MAJOR=3 -DCAS_VERSION_MINOR=1 -DCAS_VERSION=\"26.03.1.1031.release\" -Ofast -D_FORTIFY_SOURCE=2 -Wformat -Wformat-security -I/scratch/open-cas-linux-26.03.1.1031.release/modules -I/scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache -I/scratch/open-cas-linux-26.03.1.1031.release/modules/include -DCAS_KERNEL=\"6.12.0-160000.27-default\" -Werror  -DMODULE -mno-save-toc-indirect -mcmodel=large  -DKBUILD_BASENAME='"service_ui_ioctl"' -DKBUILD_MODNAME='"cas_cache"' -D__KBUILD_MODNAME=kmod_cas_cache -c -o /scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache/service_ui_ioctl.o /scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache/service_ui_ioctl.c  
/scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache/service_ui_ioctl.c: In function ‘cas_service_ioctl_ctrl’:
/scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache/service_ui_ioctl.c:275:9: error: case label does not reduce to an integer constant
  275 |         case KCAS_IOCTL_CACHE_INFO: {
      |         ^~~~
make[5]: *** [/usr/src/linux-6.12.0-160000.27/scripts/Makefile.build:229: /scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache/service_ui_ioctl.o] Error 1
make[4]: *** [/usr/src/linux-6.12.0-160000.27/scripts/Makefile.build:478: /scratch/open-cas-linux-26.03.1.1031.release/modules/cas_cache] Error 2
make[3]: *** [/usr/src/linux-6.12.0-160000.27/Makefile:1971: /scratch/open-cas-linux-26.03.1.1031.release/modules] Error 2
make[2]: *** [../../../linux-6.12.0-160000.27/Makefile:224: __sub-make] Error 2
make[2]: Leaving directory '/usr/src/linux-6.12.0-160000.27-obj/ppc64le/default'
make[1]: *** [Makefile:47: default] Error 2
make[1]: Leaving directory '/scratch/open-cas-linux-26.03.1.1031.release/modules'
make: *** [Makefile:23: modules] Error 2

The blk_mq log file contains this

### struct blk_mq_ops ops; ops.map_queue; ###
make: Entering directory '/scratch/open-cas-linux/configure.d/1_blk_mq.conf_dir'
make -C /lib/modules/6.12.0-160000.27-default/build/ M=/scratch/open-cas-linux/configure.d/1_blk_mq.conf_dir modules
make[1]: Entering directory '/usr/src/linux-6.12.0-160000.27-obj/ppc64le/default'
  CC [M]  /scratch/open-cas-linux/configure.d/1_blk_mq.conf_dir/test_mod.o
/scratch/open-cas-linux/configure.d/1_blk_mq.conf_dir/test_mod.c: In function ‘test_init_module’:
/scratch/open-cas-linux/configure.d/1_blk_mq.conf_dir/test_mod.c:7:28: error: ‘struct blk_mq_ops’ has no member named ‘map_queue’; did you mean ‘map_queues’?
    7 | struct blk_mq_ops ops; ops.map_queue;
      |                            ^~~~~~~~~
      |                            map_queues
make[3]: *** [/usr/src/linux-6.12.0-160000.27/scripts/Makefile.build:229: /scratch/open-cas-linux/configure.d/1_blk_mq.conf_dir/test_mod.o] Error 1
make[2]: *** [/usr/src/linux-6.12.0-160000.27/Makefile:1971: /scratch/open-cas-linux/configure.d/1_blk_mq.conf_dir] Error 2
make[1]: *** [../../../linux-6.12.0-160000.27/Makefile:224: __sub-make] Error 2
make[1]: Leaving directory '/usr/src/linux-6.12.0-160000.27-obj/ppc64le/default'
make: *** [Makefile:21: all] Error 2
make: Leaving directory '/scratch/open-cas-linux/configure.d/1_blk_mq.conf_dir'

I tried the development version, as well - same result.

Any ideas?

[robertbaldyga]

Oh, that's an interesting problem. KCAS_IOCTL_CACHE_INFO is defined as:

#define KCAS_IOCTL_CACHE_INFO _IOWR(KCAS_IOCTL_MAGIC, 24, struct kcas_cache_info)

where struct kcas_cache_info is quite a large structure (sizeof(struct kcas_cache_info) = 12432 bytes).

The macro _IOWR is defined as follows:

#define _IOWR(type,nr,argtype) _IOC(_IOC_READ|_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(argtype)))

and this _IOC_TYPECHECK is where things start getting interesting. It's defined as:

#define _IOC_TYPECHECK(t) \
        ((sizeof(t) == sizeof(t[1]) && \
          sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
          sizeof(t) : __invalid_size_argument_for_IOC)
#endif

where _IOC_SIZEBITS is different for different architectures. For x86_64 it's 14 bits, so just enough to represent structure of over 12kiB. However for ppc it's 13, effectively limiting the maximum size of structure that can be passed as an argument to ioctl on this architecture to 8kiB.

Majority of the memory in struct kcas_cache_info is occupied by uint16_t core_id[OCF_CORE_NUM], where OCF_CORE_NUM is 4096 by default. You can try to reduce it by setting OCF_CORE_NUM to way smaller value, so that entire structure fits within 8kiB.

When it comes to compilation errors in configure.d logs, it's completely normal, and it's nothing to worry about as long as ./configure does not report any problems. OpenCAS ./configure script automatically performs a series of compilation tests to match compatibility layer against current kernel version. Some of those tests will fail, and that's just an input for the tool.

[robertbaldyga]

I took a closer look at struct kcas_cache_info and I found that this large array of core_id could actually be replaced with way smaller bitmap. I wrote a small patch that does this change #1759. That should fix your compilation problem.

[M-Stenzel]

I took a closer look at struct kcas_cache_info and I found that this large array of core_id could actually be replaced with way smaller bitmap. I wrote a small patch that does this change #1759. That should fix your compilation problem.

Hey, this is REALLY great, yesterday I felt a little lost regarding multiple files that contain "OCF_CORE_NUM" string (I am not a C/C++ knowledgable person).
Too bad I do need a little help here - this means I need to patch each file one after another? Sorry for my "ignorance"...

[robertbaldyga]

The patch is merged to master already, so you just need to pull the master. Let me know if the compilation worked this time.

[M-Stenzel]

Great! I can confirm that the patches fixed the compilation problem!
The kernel module gets built successfully 🥇 and loads successfully on ppc64le.

[40480.302181] [ T135528] cas_cache: loading out-of-tree module taints kernel.
[40480.380545] [ T135528] 'OCF_Core' volume operations registered
[40480.380553] [ T135528] 'OCF_Cache' volume operations registered
[40480.382325] [ T135528] 'OCF Composite' volume operations registered
[40480.409493] [ T135528] 'Block_Device' volume operations registered
[40480.409641] [ T135528] Open Cache Acceleration Software Linux Version 26.06.0.1046.master (6.16.6-6.16.6-lp160.2-lucy-gcc)::Module loaded successfully 

Now I will need to extend my hardware to use the accelerator...

Thank you again!

Martin.

[M-Stenzel]

Great! I can confirm that the patches fixed the compilation problem! The kernel module gets built successfully 🥇 and loads successfully on ppc64le.

[40480.302181] [ T135528] cas_cache: loading out-of-tree module taints kernel.
[40480.380545] [ T135528] 'OCF_Core' volume operations registered
[40480.380553] [ T135528] 'OCF_Cache' volume operations registered
[40480.382325] [ T135528] 'OCF Composite' volume operations registered
[40480.409493] [ T135528] 'Block_Device' volume operations registered
[40480.409641] [ T135528] Open Cache Acceleration Software Linux Version 26.06.0.1046.master (6.16.6-6.16.6-lp160.2-lucy-gcc)::Module loaded successfully 

Now I will need to extend my hardware to use the accelerator...

Thank you again!

Martin.

O. K. Here comes an update for ppc64le

Running

casadm -S -d "/dev/disk/by-id/usb-IB-1816M_-C31_DD56419883FF9-0:0"

results in

2026-05-10T16:32:28.540536+02:00 lucy kernel: [ T4340] Inserting cache cache1
2026-05-10T16:32:28.555533+02:00 lucy kernel: [ T4340] cache1: Metadata initialized
2026-05-10T16:32:28.557527+02:00 lucy kernel: [ T4340] cache1: Successfully added
2026-05-10T16:32:28.557536+02:00 lucy kernel: [ T4340] cache1: Cache mode : wt
2026-05-10T16:32:28.557539+02:00 lucy kernel: [ T4340] Thread cas_io_1_0 started
2026-05-10T16:32:28.557542+02:00 lucy kernel: [ T4340] Thread cas_io_1_1 started
2026-05-10T16:32:28.557546+02:00 lucy kernel: [ T4340] Thread cas_io_1_2 started
2026-05-10T16:32:28.557551+02:00 lucy kernel: [ T4340] Thread cas_io_1_3 started
2026-05-10T16:32:28.557553+02:00 lucy kernel: [ T4340] Thread cas_io_1_4 started
2026-05-10T16:32:28.558542+02:00 lucy kernel: [ T4340] Thread cas_io_1_5 started
2026-05-10T16:32:28.558547+02:00 lucy kernel: [ T4340] Thread cas_io_1_6 started
2026-05-10T16:32:28.558550+02:00 lucy kernel: [ T4340] Thread cas_io_1_7 started
2026-05-10T16:32:28.558552+02:00 lucy kernel: [ T4340] Thread cas_io_1_8 started
2026-05-10T16:32:28.558557+02:00 lucy kernel: [ T4340] Thread cas_io_1_9 started
2026-05-10T16:32:28.558560+02:00 lucy kernel: [ T4340] Thread cas_io_1_10 started
2026-05-10T16:32:28.558562+02:00 lucy kernel: [ T4340] Thread cas_io_1_11 started
2026-05-10T16:32:28.558564+02:00 lucy kernel: [ T4340] Thread cas_io_1_12 started
2026-05-10T16:32:28.558566+02:00 lucy kernel: [ T4340] Thread cas_io_1_13 started
2026-05-10T16:32:28.558569+02:00 lucy kernel: [ T4340] Thread cas_io_1_14 started
2026-05-10T16:32:28.558572+02:00 lucy kernel: [ T4340] Thread cas_io_1_15 started
2026-05-10T16:32:28.558574+02:00 lucy kernel: [ T4340] Thread cas_io_1_16 started
2026-05-10T16:32:28.558578+02:00 lucy kernel: [ T4340] Thread cas_io_1_17 started
2026-05-10T16:32:28.558588+02:00 lucy kernel: [ T4340] Thread cas_io_1_18 started
2026-05-10T16:32:28.558590+02:00 lucy kernel: [ T4340] Thread cas_io_1_19 started
2026-05-10T16:32:28.558592+02:00 lucy kernel: [ T4340] Thread cas_io_1_20 started
2026-05-10T16:32:28.558594+02:00 lucy kernel: [ T4340] Thread cas_io_1_21 started
2026-05-10T16:32:28.558596+02:00 lucy kernel: [ T4340] Thread cas_io_1_22 started
2026-05-10T16:32:28.558598+02:00 lucy kernel: [ T4340] Thread cas_io_1_23 started
2026-05-10T16:32:28.558600+02:00 lucy kernel: [ T4340] Thread cas_io_1_24 started
2026-05-10T16:32:28.558602+02:00 lucy kernel: [ T4340] Thread cas_io_1_25 started
2026-05-10T16:32:28.558607+02:00 lucy kernel: [ T4340] Thread cas_io_1_26 started
2026-05-10T16:32:28.559518+02:00 lucy kernel: [ T4340] Thread cas_io_1_27 started
2026-05-10T16:32:28.559524+02:00 lucy kernel: [ T4340] Thread cas_io_1_28 started
2026-05-10T16:32:28.559526+02:00 lucy kernel: [ T4340] Thread cas_io_1_29 started
2026-05-10T16:32:28.559529+02:00 lucy kernel: [ T4340] Thread cas_io_1_30 started
2026-05-10T16:32:28.559533+02:00 lucy kernel: [ T4340] Thread cas_io_1_31 started
2026-05-10T16:32:28.559536+02:00 lucy kernel: [ T4340] Thread cas_mngt_1 started
2026-05-10T16:32:28.864538+02:00 lucy kernel: [ T4378] cache1: Metadata access size: 37 kiB
2026-05-10T16:32:29.142568+02:00 lucy kernel: [ T4378] cache1: Super block config offset : 0 kiB
2026-05-10T16:32:29.142589+02:00 lucy kernel: [ T4378] cache1: Super block config size : 2452 B
2026-05-10T16:32:29.142592+02:00 lucy kernel: [ T4378] cache1: Super block runtime offset : 128 kiB
2026-05-10T16:32:29.142596+02:00 lucy kernel: [ T4378] cache1: Super block runtime size : 4 B
2026-05-10T16:32:29.142600+02:00 lucy kernel: [ T4378] cache1: Reserved offset : 256 kiB
2026-05-10T16:32:29.142603+02:00 lucy kernel: [ T4378] cache1: Reserved size : 2048 kiB
2026-05-10T16:32:29.142616+02:00 lucy kernel: [ T4378] cache1: Part config offset : 2304 kiB
2026-05-10T16:32:29.142618+02:00 lucy kernel: [ T4378] cache1: Part config size : 64 kiB
2026-05-10T16:32:29.142620+02:00 lucy kernel: [ T4378] cache1: Part runtime offset : 2560 kiB
2026-05-10T16:32:29.142623+02:00 lucy kernel: [ T4378] cache1: Part runtime size : 64 kiB
2026-05-10T16:32:29.142625+02:00 lucy kernel: [ T4378] cache1: Core config offset : 2688 kiB
2026-05-10T16:32:29.142627+02:00 lucy kernel: [ T4378] cache1: Core config size : 512 kiB
2026-05-10T16:32:29.142629+02:00 lucy kernel: [ T4378] cache1: Core runtime offset : 3712 kiB
2026-05-10T16:32:29.142631+02:00 lucy kernel: [ T4378] cache1: Core runtime size : 1216 kiB
2026-05-10T16:32:29.142632+02:00 lucy kernel: [ T4378] cache1: Core UUID offset : 4992 kiB
2026-05-10T16:32:29.142635+02:00 lucy kernel: [ T4378] cache1: Core UUID size : 16384 kiB
2026-05-10T16:32:29.142636+02:00 lucy kernel: [ T4378] cache1: Cleaning offset : 37760 kiB
2026-05-10T16:32:29.142638+02:00 lucy kernel: [ T4378] cache1: Cleaning size : 2834048 kiB
2026-05-10T16:32:29.142640+02:00 lucy kernel: [ T4378] cache1: LRU list offset : 2871808 kiB
2026-05-10T16:32:29.142642+02:00 lucy kernel: [ T4378] cache1: LRU list size : 2125632 kiB
2026-05-10T16:32:29.142644+02:00 lucy kernel: [ T4378] cache1: Collision offset : 4997504 kiB
2026-05-10T16:32:29.142646+02:00 lucy kernel: [ T4378] cache1: Collision size : 2361792 kiB
2026-05-10T16:32:29.142648+02:00 lucy kernel: [ T4378] cache1: List info offset : 7359360 kiB
2026-05-10T16:32:29.142650+02:00 lucy kernel: [ T4378] cache1: List info size : 1889216 kiB
2026-05-10T16:32:29.142653+02:00 lucy kernel: [ T4378] cache1: Hash offset : 9248640 kiB
2026-05-10T16:32:29.142655+02:00 lucy kernel: [ T4378] cache1: Hash size : 236160 kiB
2026-05-10T16:32:29.142658+02:00 lucy kernel: [ T4378] cache1: Cache line size: 4 kiB
2026-05-10T16:32:29.142660+02:00 lucy kernel: [ T4378] cache1: Metadata size on device: 9484800 kiB
2026-05-10T16:32:29.142663+02:00 lucy kernel: [ T4378] cache1: Metadata alock size: 16385 kiB
2026-05-10T16:32:29.143537+02:00 lucy kernel: [ T4378] cache1: Metadata access size: 236152 kiB
2026-05-10T16:32:29.224631+02:00 lucy kernel: [ T4378] Thread cas_cl_cache1 started
2026-05-10T16:32:29.224668+02:00 lucy kernel: [ T4378] cache1: Policy 'always' initialized successfully
2026-05-10T16:33:53.748537+02:00 lucy kernel: [ T4378] cache1: Done saving cache state!
2026-05-10T16:33:53.829533+02:00 lucy kernel: [ T4378] cache1: Cache attached
2026-05-10T16:33:53.829549+02:00 lucy kernel: [ T4378] cache1: Successfully attached
2026-05-10T16:33:53.829554+02:00 lucy kernel: [ T4340] [Open-CAS] Adding device /dev/disk/by-id/usb-IB-1816M_-C31_DD56419883FF9-0:0 as cache cache1
2026-05-10T16:33:53.829568+02:00 lucy kernel: [ T4340] [Open-CAS] [Classifier] Initialized IO classifier

Very happy about that!

Too bad I am unable to use a backend device, this is the output of

casadm -A -d /dev/disk/by-id/wwn-0x3044564198836690 -i 1

2026-05-10T16:36:51.092578+02:00 lucy kernel: [ T4378] cache1: Core core1 is zero size
2026-05-10T16:36:51.093531+02:00 lucy kernel: [ T4378] cache1: Adding core core1 failed

Could it be due to the fact that this is a USB device? I wanted to check first, whether it is worth purchasing a more professional hardware setup...

Here https://open-cas.com/getting_started_open_cas_linux.html it states "The output should return the cache instance number, ...". In my case there is no output, nor an error or warning either.

Martin.