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

Richard Zawaski zski128 at yahoo.com
Thu Aug 4 12:01:49 CDT 2011

Those systems are BSD/Linux correct? DeDup on Solaris worked great in our
case. Saved lots of IO to the disk and actually sped up file access. DeDup
with ZFS on anything else but Solaris I would not trust.
From: JP Hindin <jplist2008 at kiwigeek.com>
The Rescue List <rescue at sunhelp.org>
Sent: Thursday, August 4, 2011 12:36 PM
Subject: Re: [rescue] FreeBSD and ZFS, was Re: 3ware raid

On Thu, 4 Aug 2011,
N. Miller wrote:
> 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.

"accidentally" ended up having de-dupe turned on in our various Nexenta
arrays and it caused no end of troubles with false disk failures,
data loss
and all sorts of crazy stuff.
As soon as we verified the issue and turned
de-dupe off the issues all
vanished and we've had a set of solid Nexentas ever
since (12mos and
counting on three Nexentas with about 120T of storage between

I know it's anecdotal, but it was a total nightmare for us.

- JP
rescue list -

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