Protection level +2d:1n or +4d:1n on 4 nodes

Hello Yasu,

The protection percentage is the same for +2d:1n and +4d:1n.  The space should be the same as long as all the drives are the same size & speed.  

Thank you for reply.
I find Isilon sizer shows performance of H500 (480GB) v8.2.2 as below;
Sequential Read
+2d:1n = 6.81 GBps 16 threads
+3d:1n = 6.47 GBps 16 threads
+4d:1n = 6.06 GBps 16 threads
So I will take +2d:1n.

Regards,

YASU

There are two impacts to choosing a higher protection level:

1. Performance. There is a small but measurable performance impact to choosing higher protection levels.
2. Efficiency. In your case, the overhead on large files is the same, but the overhead on small files is larger because you need 4 FEC blocks regardless of whether you have 12 data blocks (12+4) or 1 data block (1+4).

In general, it is best to choose the recommended level. The system uses a "failure simulator" to generate statistical data and uses that data to determine the lowest protection level that guarantees an MTTDL of at least 5000 years. For Gen 6 nodes, that generally results in +2d:1n for smaller cluster/drive sizes and +3d+1n1d for larger clusters and drive sizes. Unless there are other compelling reasons/requirements to do so, using the recommended value is the right thing to do.

Thank you for reply.
Okay I will take +2d:1n and check data 5000 years later.

Regards,

YASU