Are regular smart tests safe? And smart logs capacity, location

Hi!

I'm curious about correlation between regular SMART tests (long and
short) and disk health. When smart tests are running HDD emits strange
sounds, and I do not know what is going on inside HDD, maybe only vendor
does. Does it reduce hdd health? Do you have such statistics?

My disks pass 4 short and 1 long test per month, so smart logs are
getting bigger with 5 strings every month. Are this logs stored on hdd,
or somewhere on my PC? If they are stored on disk, how much regular disk
can store (about 100, about 1000?)?

Kind regards,
Yan

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