[rescue] FreeBSD and ZFS, was Re: 3ware raid

[N. Miller]

On Jul 27, 2011, at 1:45 PM, Richard Zawaski wrote:

> If you want all the coolness that ZFS provides then use OpenSolaris which
supports all the features of the latest ZFS version, like dedup, etc. FreeBSD
works fine for ZFS but you may find the performance a bit lacking. Also, ZFS
works best with a JBOD setup.
>

You need to be very careful with dedup.  IMO, I would never implement it
without first doing extensive tests with a copy of the real data I expected to
see in production.  You need lots of RAM on top of the normal "lots" of RAM
required by ZFS, because the entire dedup table is kept in resident memory.

Also, you can't revert without doing a dataset (or maybe pool, not sure if
this is a pool-wide or dataset level config) rebuild.  Example: you can turn
on compression, anything written to the dataset while compression is on will
be compressed.  You can then turn off compression and anything written to disk
will not be compressed, but compressed data can still be read, etc.  With
dedup, it's ON, and you can only turn it off by sending all the data to a
dataset with dedup OFF.

We received this warning from Richard Elling in ZFS class at LISA last
winter.