Likely Readynas 3-series

janpeter wrote:
1) I wonder how big role has the ECC RAM-memory for data integrity, which comes with upgrade to 5-series. I understand it improves somehow the bit-rot protection and more. Would be good with some brief explanation of reference to where it can be found...

ECC RAM is a must-have in data center servers.

The main thing to keep in mind is that bit-rot protection in ZFS and BTRFS protects the data on the disk. It doesn't protect the data while its in RAM (either on the way to the disk on a write, or on the way to the user after a read). Clear evidence of true "bit rot" is pretty hard to find, but everyone agrees that memory errors in data centers occur (the ECC memory reports them!).

Memory failures are relatively rare, but when one does occur the odds of it resulting in data corruption is about 10%. That is based on this study: http://research.cs.wisc.edu/adsl/Public ... fast10.pdf). This particular study focuses on ZFS, but potentially is applicable to BTRFS as well (since AFAIK neither implementation guards against memory failure). In a file server application, about 3.6% of the time a single bit flip resulted in corrupted writing of the data. Odds of a corrupted read was about 7%.

How much this matters depends on how frequent memory failures actually are. There are a couple of studies on these failures, but I find it difficult to draw any simple conclusions from them - other than that memory failures do occur, and that ECC fixes almost all of them. One of those studies is here: http://www.cs.toronto.edu/~bianca/paper ... rics09.pdf

I don't have a NAS with ECC memory myself. FWIW bit rot has never been reported in my RN102 or my RN202, and I don't have any clear evidence of data corruption in any of my NAS from any cause.