On 09/24/10 11:26, Peter Taps wrote:> Folks,
>
> One of the zpool properties that is reported is "dedupditto."
However, there is no documentation available, either in man pages or anywhere
else on the Internet. What exactly is this property?
>
> Thank you in advance for your help.
>
> Regards,
> Peter
>
I found it documented in man zpool:
dedupditto=number
Sets a threshold for number of copies. If the reference
count for a deduplicated block goes above this thres-
hold, another ditto copy of the block is stored automat-
ically. The default value is 0.
--------
It seems a bit counter-intuitive to start with. The purpose of dedup is
to remove
copies of blocks. However, if there are say 50 references to the same
block and that block gets checksum errors then all 50 references are bad.
So this is another form of redundancy, by telling zfs to store an additional
copy say a specific number of references.
Neil.