/sys/block/sdx/device/rescan What is it for ?

Hi

First as I am not an expert, please try to answer for regular user.

In a context dealing with cloud VM and virtual storage upgrade,
after increasing volume size from provider's part

I've eared about :
Code:# echo 1 > /sys/block/sdx/device/rescanIn order the system to detect the new parameters of changed disk.

Then to intent to understand what's about, I've tried :
Code:$ su -
# cat /sys/block/sda/device/rescan
cat: /sys/block/sda/device/rescan: Permission non accordee

# ls -l /sys/block/sda/device/rescan
--w------- 1 root root 4096 aout 22 11:01 /sys/block/sda/device/rescanroot is only allowed to write it, that seems a bit strange to me.

I didn't found man/info section about "rescan"

So should be kind if someone mights tell me a few about that file.
Is there some risks using that ?

Thanks.