Storage IO issuance and RAID5 write penalty issues

9 disks with 128kb striping depth RAID5

A 100kb small IO on the host needs to be written to storage. Because it is less than half of the number of disks, read-rewrite is used. Why is the way of generating new parity data different from read-rewrite and reconstruction write? What is the reason for different IO Is the size used for read-rewrite or reconstruction?

A small 100kb IO on the host needs to be written to the storage. This IO is written to the hard disk in a read/write mode, but should the next 100kb IO be written to another stripe or the remaining space of the stripe? What is the actual chunk size written to the hard disk?

Thanks