What is purpose of /dev/mmcblk2boot devices?

[greenais]

Please give me a tip - what is purpose of /dev/mmcblk2boot block devices created?
Quite small size - 4MB - ones, do they serve to something u-boot needs at boot time?
There are no records for them in fstab so I assume they are created by zram, but what happens to them after boot when they aren't needed anymore?

 

Board Orangepi 3LTS with bookworm minimal
 

Also as a matter of wondering - why there are two zram devices: one of 1/2 of RAM (as usual) and another of quite small 50MB only, what is it for?

 

 

root@heaven:~# fdisk -l
<redacted>

Disk /dev/mmcblk2boot0: 4 MiB, 4194304 bytes, 8192 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/mmcblk2boot1: 4 MiB, 4194304 bytes, 8192 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

<redacted>

Disk /dev/zram0: 987,53 MiB, 1035497472 bytes, 252807 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes


Disk /dev/zram1: 50 MiB, 52428800 bytes, 12800 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

 

[Werner]

 

18 minutes ago, greenais said:

/dev/mmcblk2boot

Good question. Have you tried to use binwalk oder strings on it?

 

18 minutes ago, greenais said:

e two zram devices:

One is for ramlog and should be mounted to /var/log. The other is zram which by default is half of your actual memory.

In the early days SBCs hat very limited memory, so using zram was a simple way to increase that by sacrificing some cpu resources. Nowadays SBCs come with a lot more memory and some may not even need zram anymore. Depending on your setup you can disable it as well. Check /etc/default/armbian-* files.

[greenais]

1 hour ago, Werner said:

One is for ramlog and should be mounted to /var/log. The other is zram which by default is half of your actual memory.

In fact in image's default fstab they aren't mounted so those probably could be assumed as a kind of waste of RAM this way? Or there is chance that they actually mounted somewhere else but fstab?
 

root@heaven:~# cat /etc/fstab
# <file system>                                 <mount point>   <type>  <options>                                      <dump>   <pass>
tmpfs                                           /tmp            tmpfs   defaults,nosuid                                00
UUID=fb077685-a428-49f2-b013-287dc5fc9672       /               ext4    defaults,noatime,commit=120,errors=remount-ro,x-gvfs-hide       0       1

 

Thank you for tip regarding /var/log, I was suspecting that it should be there as soon as device created.

 

 

1 hour ago, Werner said:

Have you tried to use binwalk oder strings on it?

Do you mean to inspect with binwalk/strngs those devices in hope to find out what is there? I'd gave a try - there is nothing:

root@heaven:~# binwalk /dev/mmcblk2boot0
DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
root@heaven:~# binwalk /dev/mmcblk2boot1
DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
root@heaven:~# strings /dev/mmcblk2boot0
root@heaven:~#

 

They also can't be mounted - dmesg excerpt:

[390869.014377] F2FS-fs (mmcblk2boot0): Magic Mismatch, valid(0xf2f52010) - read(0x0)
[390869.014508] F2FS-fs (mmcblk2boot0): Can't find valid F2FS filesystem in 1th superblock

Magic mismatch - mystic things unsolved)

[Werner]

2 minutes ago, greenais said:

In fact in image's default fstab they aren't mounted so those probably could be assumed as a kind of waste of RAM this way?

Have you checked "mount" command to list actualy mounts?  I am quite confident mount is happening by the ramlog service and is not integrated into fstab.

some more background: sdcards have a limited amount of writes until its cells die. Since everytime some service or whatever writes some logs this issues a write event. To drastically increase the lifespan of the microsd log entries are buffered to (compressed) memory and then recurringly written all at once.

[greenais]

9 minutes ago, Werner said:

I am quite confident mount is happening by the ramlog service and is not integrated into fstab.

 

You are completely right - at least 50MB one is there

/dev/zram1 on /var/log type ext4 (rw,nosuid,nodev,noexec,relatime,discard)

But big 987MB /dev/zram0 isn't at all - so it looks like it's useless and could be removed from zram config, right?

Both mystic /dev/mmcblk2bootX are still in question

[Werner]

2 hours ago, greenais said:

987MB

I explained above what zram is created for. OPi3LTS should have 2G  of memory, so having 1G of zram makes perfect sense here.

[greenais]

28 minutes ago, Werner said:

what zram is created for

Yes, but since this created device isn't mounted anywhere it makes no sense - no service or whatever could use it anyway, what definitely turns this creature into just waste of RAM for nothing, am I wrong?