While checking why USB disk performance on RouterOS 6.34.4 is so bad, I found ext3 format is default, and the partition is bady misaligned, so causes write amplification:

# fdisk -l /dev/sdb
Disk /dev/sda: 14.9 GiB, 16013942784 bytes, 31277232 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
Disklabel type: dos
Disk identifier: 0x6f5c0eca

Device Boot Start End Sectors Size Id Type
/dev/sda1 * 1 31277231 31277231 14.9G 83 Linux

If I format the same disk from another Linux system, the partition starts at 1MB, giving better write performance:

# fdisk -l /dev/sda
Disk /dev/sda: 14.9 GiB, 16013942784 bytes, 31277232 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
Disklabel type: dos
Disk identifier: 0xa7448d48

Device Boot Start End Sectors Size Id Type
/dev/sda1 2048 31277231 31275184 14.9G 83 Linux

However, I have to format it ext3, as ext4 is not supported in RouterOS!

@MikroTik, ext3 is not supported in the Linux Kernel and has been deprecated for 10 years now and has poor performance as directories fill up, so please fix this.

Second, why not allow f2fs as an alternative? This filesystem is optimised for flash media and is used on Android phones everywhere.