Hacker News Reader

Comment by jeroenhd | Hacker News Reader

The data security and rot resilience only goes for systems with ECC memory. Correct data with a faulty checksum will be treated the same as incorrect data with a correct checksum.

Windows has its own extended filesystem through Storage Spaces, with many ZFS features added as lesser used Storage Spaces options, especially when combined with ReFS.

View on HN

This has nothing to do with ZFS as a filesystem. It has integrity verification on duplicated raid configurations. If the system memory flips a bit, it will get written to disk like all filesystems. If a bit flips on a disk, however, it can be detected and repaired. Without ECC, your source of truth can corrupt, but this true of any system.

Please stop repeating this, it is incorrect. ECC helps with any system, but it isn't necessary for ZFS checksums to work.

On zfs there is the ARC (adaptive read cache), on non-zfs systems this "read cache" is called buffer, both reside in memory, so ECC is equally important for both systems.

Rot means changing bits without accessing those bits, and that's ~not possible with zfs, additionally you can enable check-summing IN the ARC (disabled by default), and with that you can say that ECC and "enterprise" quality hardware is even more important for non-ZFS systems.

>Correct data with a faulty checksum will be treated the same as incorrect data with a correct checksum.

There is no such thing as "correct" data, only a block with a correct checksum, if the checksum is not correct, the block is not ok.

"data security and rot resilience only goes for systems with ECC memory."

No. Bad HDDs/SSDs or bad SATA cables/ports cause a lot more data corruption than bad RAM. And ZFS will correct these cases even without ECC memory. It's a myth that the data healing properties of ZFS are useless without ECC memory.

Precisely this. And don’t forget about bugs in virtualization layers/drivers — ZFS can very often save your data in those cases, too.

I once managed to use ZFS to detect a bit flip on a machine that did not have ECC RAM. All python programs started crashing in libpython.so on my old desktop one day. I thought it was a bug in ZFS, so I started debugging. I compared the in-memory buffer from ARC with the on-disk buffer for libpython.so and found a bit flip. At the time, accessing a snapshot through .zfs would duplicate the buffer in ARC, which made it really easy to compare the in-memory buffer against the on-disk buffer. I was in shock as I did not expect to ever see one in person. Since then, I always insist on my computers having ECC.

Reply on news.ycombinator.com