# Node selection ratio

Why is the ratio of nodes selected from 80 to 29? How did 80 and 29 come.Why the redundancy multiple is 2.76

80 is initial ammount of pieses that Tardigate make when file is uploaded.

and to download file you need only 29 pieses from this 80.

Is the value 29 also required by tardigrate? Why is the data redundancy multiple of 2.76? Is this related to durability?

Hello @CZC,
Welcome to the forum!

3 Likes

Sorry, I still canâ€™t understand why the data redundancy is 2.76 times and why 29 nodes out of 80 nodes are selected to restore files

this is minimum pises count that needed to restore file.

How did it get this minimum number? I want to know how the principle is realized, thank you

this is described in details in the Whitepaper

But you can read a short version in the blog

1 Like

Guys, youâ€™re running in circles here. The OP asked, why 80 and 29 was chosen, and not 90 and 35 or whatever other values. I didnâ€™t read the whitepaper, I only searched for â€ś29â€ť and there were no matches related to this question.

Yes, I just want to know how this data is obtained, because the white paper only talks about node churn rate and expansion factor, which are related to file durability, but none of these can solve my doubts. 29 I may not understand how this number is derived, how the redundancy 2.76 times is derived, and how the erasure coding technology is implemented in this system, I may not understand, so I need someone to explain to me, I will Thank you very much.

I believe at least one of the links will explain the difference between 2 pieces out of 4 and 20 pieces out of 40. The expansion factor is the same in both cases but the durability is different. One of these links should explain that. So could you please be a bit more specific what exactly you want to know?

Edit: As I can see the last link from Alexey is explaining exactly that point and it also explains how to find the sweet spot between low repair costs and low used space costs.

So the only information missing is the piece size. We figured out that 29 in combination with 64MB blocks is not optimal to get best performance from storage nodes. We might want to take that into account in the future.

3 Likes

Thank you for your answer. Can I understand that the minimum number of restore pieces of 29 is obtained through testing? Or maybe it is obtained by some kind of algorithm. I just donâ€™t understand why this value is not other values. Is this value also obtained by calculating the most combined point of maintenance cost and storage cost?

Sorry, I think I know why the value is 29, because I donâ€™t understand the specifics of erasure coding technology. These values are just for better data restoration. I learned from your companyâ€™s official blog. Thank you for your answers, thank you very much.

1 Like

29 pieses is related to Read Salamon Encryption to get aal needed information from pieses to restore file you need minimum 29 pieses, thay contain all neded information to decrypt them back to file. if less then it not posible anymore to decrypt it back.