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Is the issue with ZFS deduplication really due to the fact that it is done online ? From what I understand the way that ZFS works, the amount of ram used to kee
by mrighele 7y ago
Is the issue with ZFS deduplication really due to the fact that it is done online ? From what I understand the way that ZFS works, the amount of ram used to keep deduplication metadata would be necessary even if the deduplication was done offline, i.e. it is necessary also for read operations, not only for write operations.
- sliken 7y agoI believe the ZFS deduplication consumes a ton of ram (somewhere around 1GB of ram per TB of disk) to keep the block checksums in ram. Said list is checked for every block write. I don't believe it's necessary to check for reads, since the file metadata already tells you which blocks to look for. As a result ZFS with deduplication on uses a ton of ram and has slow writes. This is so big an impact that most folks just turn it off, despite the tempting lure of "free" disk space.