Difference between EC and Three-Copy

little_fish · Created Oct 26, 2021 11:45:22

Dear Axe,

As shown in Table 1, the space utilization in EC mode is higher than that in multi-copy mode. Therefore, the EC redundancy protection mechanism is recommended. Thanks.

**Table 1** Differences between EC and multi-copy
Item	EC (N+M)	Three-Copy
Space Utilization	At least 66% The utilization increases as the value of N increases.	33%
Reliability	Cabinet-level security: The system can tolerate the failures of M cabinets or M nodes. Server-level security: The system can tolerate the failures of M nodes or M disks.	The system can tolerate the failures of any two cabinets (cabinet-level reliability), two nodes, or two disks. Cabinet-level security: A maximum of two faulty cabinets are allowed. Server-level security: A maximum of two faulty nodes are allowed.
Rebuilding	Data needs to be decoded by EC to obtain the target fragments.	Data is copied from another disk and then rebuilt.
SSD cache service life	When the service I/Os are the same and the number of invalid I/Os is small, the total number of writes is 2/3 of that in the three-copy storage mode, and the SSD cache consumption is small.	When the service I/Os are the same and the number of invalid I/Os is large, the total number of writes is 1.5 times that of EC, and the SSD cache consumption is high.

little_fish · Created Oct 26, 2021 11:45:22

Dear Axe,

As shown in Table 1, the space utilization in EC mode is higher than that in multi-copy mode. Therefore, the EC redundancy protection mechanism is recommended. Thanks.

**Table 1** Differences between EC and multi-copy
Item	EC (N+M)	Three-Copy
Space Utilization	At least 66% The utilization increases as the value of N increases.	33%
Reliability	Cabinet-level security: The system can tolerate the failures of M cabinets or M nodes. Server-level security: The system can tolerate the failures of M nodes or M disks.	The system can tolerate the failures of any two cabinets (cabinet-level reliability), two nodes, or two disks. Cabinet-level security: A maximum of two faulty cabinets are allowed. Server-level security: A maximum of two faulty nodes are allowed.
Rebuilding	Data needs to be decoded by EC to obtain the target fragments.	Data is copied from another disk and then rebuilt.
SSD cache service life	When the service I/Os are the same and the number of invalid I/Os is small, the total number of writes is 2/3 of that in the three-copy storage mode, and the SSD cache consumption is small.	When the service I/Os are the same and the number of invalid I/Os is large, the total number of writes is 1.5 times that of EC, and the SSD cache consumption is high.

user_4397771 · Created Oct 27, 2021 10:08:24

Good

Axe_Z · Created Oct 27, 2021 11:23:37

Thanks.

Difference between EC and Three-Copy

Recommended answer

Third Party’s Trade Secret

My Followers

Enterprise

Consumer

Corporate

Carriers

Difference between EC and Three-Copy

Recommended answer

Third Party’s Trade Secret

My Followers