Method and system for storing a file on a plurality of servers

1. A method for storing a first file (Δ 1 ) on a plurality of servers (S 1 , S 2 , . . . , S n ), wherein the number of servers (S 1 , S 2 , . . . , S n ) is n and the maximum number of servers (S 1 , S 2 , . . . , S n ) which may fail is t, including a predefined number b of byzantine failures and a number t−b of crashes of the servers (S 1 , S 2 , . . . , S n ), and wherein n equals 2t+b+1,

the method comprising:

a) Dividing the first file (Δ 1 ) into a plurality of chunks (C 1 , C 2 , . . . , C n ), wherein the number of chunks (δ 1 ) is equal to or greater than the number of servers n,

b) Sending n chunks of the first file (Δ 1 ) to the n servers (S 1 , S 2 , . . . , S n ), wherein one chunk is sent to each server (S 1 , S 2 , . . . , S n ),

c) Determining a number of replies r from the n servers (S 1 , S 2 , . . . , S n ) indicating successful storage of the respective chunks,

d) Checking if the number of replies r matches a terminating condition (TC),

e) Generating, when the number of replies r does not match the terminating condition, a new file (Δ 2 ) based on one or more chunks of the first file (Δ 1 ), a reconstruction threshold (m 1 ) of the first file (Δ 1 ) and the number of replies r, and

f) Performing steps a)-e) with the new file (Δ 2 ), until the terminating condition in step d) is fulfilled,

wherein the terminating condition (TC) is based on the difference between the reconstruction thresholds of the new file (Δ 1 , Δ 2 , . . . , Δ k ) of step e) and the first file of step a) and the maximum number of servers t which may fail.

2. The method according to claim 1 , wherein in step a) when the number of generated chunks (C 1 , C 2 , . . . , C n ) is greater than the number of servers n, generating additional chunks, wherein the number of additional chunks is dependent on the number of servers (t) which may fail and a reconstruction threshold (m 1 , m 2 , . . . ) for the file (Δ 1 ).

3. The method according to claim 1 , wherein for the reconstruction threshold (m) is based on an estimated number of responsive servers (S 1 , S 2 , . . . , S n ).

4. The method according to claim 3 , wherein the estimated number is greater than a sum of byzantine servers b and servers t−b that may fail.

5. The method according to claim 2 , wherein the total number of chunks in step a) is

2 t+th,

wherein t is the maximum number of servers that may fail and th is the reconstruction threshold for the file.

6. The method according to claim 1 , wherein the one or more chunks for generation of the new file (Δ 2 ) are solely-based on one or more of a prior non-sent remaining chunks.

7. The method according to claim 1 , wherein the one or more chunks for generation of the new file (Δ 2 ) are only generated when the termination condition (TC) is not matched.

8. The method according to claim 1 , wherein the generation of the new file (Δ 2 ) is performed by concatenating one or more chunks for generation of the new file.

9. The method according to claim 1 , wherein a timeout threshold is used when determining the number of replies according to step c), wherein the timeout threshold starts after a predetermined number of received replies, and the predetermined number of replies is the number of replies needed for reconstruction of the file.

10. The method according to claim 9 , wherein the timeout threshold is dynamically adapted in each round of steps a)-e), wherein the adaption is based on at least one of connection conditions between a writer of the file and the servers (S 1 , S 2 , . . . , S n ) and server conditions.

11. The method according to claim 10 , wherein adaption information is encoded in the replies from the servers (S 1 , S 2 , . . . , S n ).

12. The method according to claim 1 , wherein the termination condition (TC) is fulfilled when one of the reconstruction threshold (m 2 , m 3 ) for a file (F, Δ 1 ) of an actual round with regard to rounds of steps a)-e) is greater than or equal to the reconstruction threshold (m 1 , m 2 , . . . ) of the prior round and the number of rounds has exceeded the number of servers (t) that might be fail.

13. The method according to claim 1 , wherein the new file (Δ 2 ) is generated based on the one or more chunks (C 1 ) of a prior non-sent remaining chunks.

14. A system for storing a first file (Δ 1 ) on a plurality of servers (S 1 , S 2 , . . . , S n ), wherein the number of servers (S 1 , S 2 , . . . , S n ) is n and the maximum number of servers (S 1 , S 2 , . . . , S n ) which may fail is t, preferably including a predefined number b of byzantine failures and a number t−b of crashes of the servers (S 1 , S 2 , . . . , S n ), and wherein n equals 2t+b+1, the system comprising one or more processors which, alone or in combination, are configured to provide for execution of the following steps:

dividing the first file (Δ 1 ) into a plurality of chunks (C 1 , C 2 , . . . , C n ), wherein the number of chunks (δ 1 ) is equal to or greater than the number of servers n,

sending n chunks of the first file (Δ 1 ) to the n servers (S 1 , S 2 , . . . , S n ), wherein one chunk (C 1 , C 2 ) is sent to each server (S 1 , S 2 , . . . , S n ),

determining a number of replies r from the n servers (S 1 , S 2 , . . . , S n ) indicating successful storage of the respective chunks (C 1 , C 2 ),

checking whether the number of replies r matches a terminating condition (TC),

generating a new file (Δ 2 , Δ 3 ) based on one or more chunks (C 1 , C 2 ) of the first file (Δ 1 ), a reconstruction threshold (m 1 , m 2 , . . . ) of the first file and the number of replies r, and

operating recursively the dividing, the sending, the determining, the checking and the generating steps with a new file (Δ 2 ), until the terminating condition is fulfilled,

wherein the terminating condition (TC) is based on the difference between the reconstruction thresholds of the new file (Δ 2 , . . . , Δ k ) and the first file and the maximum number of servers t which may fail.