Unable to set group_thread_cnt using mdadm.conf

[Franco Martelli <martellif67@gmail.com>]

Hello,

I've a RAID5 array on Debian 13:

~$ cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [linear] [raid0] [raid1] [raid10]
md0 : active raid5 sda1[0] sdc1[2] sdd1[3](S) sdb1[1]
       1953258496 blocks super 1.2 level 5, 512k chunk, algorithm 2 
[3/3] [UUU]

unused devices: <none>

~# mdadm --version
mdadm - v4.4 - 2024-11-07 - Debian 4.4-11

the issue is that I can't set group_thread_cnt if I use the syntax 
described in mdadm.conf(5) man-page:

…
SYSFS name=/dev/md/raid5 group_thread_cnt=4 sync_speed_max=1000000
SYSFS uuid=bead5eb6:31c17a27:da120ba2:7dfda40d group_thread_cnt=4 
sync_speed_max=1000000

my "mdadm.conf" is:

~$ grep -v '^#' /etc/mdadm/mdadm.conf


HOMEHOST <system>

MAILADDR root

ARRAY /dev/md/0  metadata=1.2 UUID=8bdf78b9:4cad434c:3a30392d:8463c7e0
    spares=1


SYSFS name=/dev/md/0 group_thread_cnt=8
SYSFS uuid=8bdf78b9:4cad434c:3a30392d:8463c7e0 sync_speed_max=1000000


after I makes changes to the file "mdadm.conf" I rebuild the initramfs 
image file and reboot. The thing that seems strange to me is that the 
other item I set (sync_speed_max) is changed accordingly, only 
"group_thread_cnt" fails to set (it's always ==0):

~$ cat /sys/block/md0/md/group_thread_cnt
0
~$ cat /sys/block/md0/md/sync_speed_max
1000000 (system)

Why "sync_speed_max" is set while "group_thread_cnt" it is not? Any clue?

Thanks in advance, kind regards.
--
Franco Martelli