Re
viewtopic.php?p=1287#p1287As I understand it …
If the state of a three-disk RAID-Z1 pool becomes
UNAVAIL with
insufficient replicas, and if a dataset in that pool always had
copies=3 :
- the one remaining disk might (should?) include one copy of each block of the dataset
- import would be impossible
– the
overriding effect of (b) would make it extraordinarily difficult to access the directories, files and metadata in a user-friendly way. I might think of part of the one remaining disk as
all files without a file system.
In this situation I guess that an expert might make some use of
zdb, but I shouldn't expect easy or complete recovery of data.
In a nutshell:
- copies=3 at the dataset level should not be viewed as a fallback where there's risk of insufficient replicas at the pool level.
Further reading/discussionUnrelated to the copies property:
RAID-Z on-disk formatRelating to copies:
Ditto Blocks - The Amazing Tape Repellent (Flippin' off bits) (2006-05-12) – an old post, but it helped me to visualise ZFS allocation for ditto blocks.