Re:FreeBSD and ZFS
by takeda on Saturday February 27, 2016 @01:14PM
(#11187868)
FreeNAS people seem to mix up what's recommended vs what's required.
The whole myth that ZFS requires ECC memory comes from them, but in reality ECC is as much helpful with ZFS as with any other FS. It's not that ZFS will start destroying your data if you don't have ECC. It's just that ZFS provides guarantees, but it can't help much if data is corrupted in memory, but any other filesystem will also be affected in that scenario.
Similarly with 8GB. You can actually run ZFS on 1GB, but the more RAM you have the better. ZFS has ARC (Adaptive Replacement Cache[1]) which speeds up read access by storing in RAM most frequently accessed data.
Not running ARC won't affect safety of your data, it's just that you'll get worse performance.
There are some warts ZFS (and most likely COW file systems) have. For example until ZFS will have a defragmenting tool (doesn't looks like anyone is working on it) you don't want ever to use more than 80% of your disk. If you do, you'll permanently reduce performance of the pool and currently the only fix would be to backup all the data, wipe disk and restore it (this effectively will defragment it).
Another issue is that deduplication in ZFS is essentially useless. It requires obscene amount of RAM to be used, and if you enable it with less, it'll drastically reduce performance as well. Instead of deduplication it's better to just enable compression.
The whole myth that ZFS requires ECC memory comes from them, but in reality ECC is as much helpful with ZFS as with any other FS. It's not that ZFS will start destroying your data if you don't have ECC. It's just that ZFS provides guarantees, but it can't help much if data is corrupted in memory, but any other filesystem will also be affected in that scenario.
Similarly with 8GB. You can actually run ZFS on 1GB, but the more RAM you have the better. ZFS has ARC (Adaptive Replacement Cache[1]) which speeds up read access by storing in RAM most frequently accessed data.
Not running ARC won't affect safety of your data, it's just that you'll get worse performance.
There are some warts ZFS (and most likely COW file systems) have. For example until ZFS will have a defragmenting tool (doesn't looks like anyone is working on it) you don't want ever to use more than 80% of your disk. If you do, you'll permanently reduce performance of the pool and currently the only fix would be to backup all the data, wipe disk and restore it (this effectively will defragment it).
Another issue is that deduplication in ZFS is essentially useless. It requires obscene amount of RAM to be used, and if you enable it with less, it'll drastically reduce performance as well. Instead of deduplication it's better to just enable compression.
[1] https://en.wikipedia.org/wiki/Adaptive_replacement_cache