On 20.10.09 21:26, Adam Leventhal wrote: >>> The second allows the administrator to select a threshhold afterwhich >>> 2 copies of a block are stored rather than 1. For example, if many >>> duplicate blocks exist deduplication would reduce that count to just 1; >>> at some threshhold, it becomes desirable to have multiple copies to >>> guard against the multiplied effects of the loss of a single block. >>> The default value is '100'. >> Is it actually necessary to expose this tunable ? Given there is already a >> per dataset copies property how does this interact with that ? > > Good questions. > > The per-dataset ncopies property is obeyed in that if one were to dedup many > blocks with ncopies set to 2 there would result in 2 copies total after > deduplication. > > The 'dedupditto' property guides what we're calling auto-ditto in which ZFS > chooses to store an additional copy once some threshhold is reached. This is > independent of the per-dataset 'ncopies' property.
What does happen to the auto-ditto copies once reference count drops below threshold? Are auto-ditto-copies freed immediately or when reference count drops below e.g. half-threshold or never? Victor
