EBS snapshot backups from a FreeBSD zfs file system: zpool freeze?

[Jeremy Chadwick]

On Thu, Jul 04, 2013 at 09:06:57AM +0100, Steven Hartland wrote:
> ----- Original Message ----- From: "Berend de Boer"
> <berend at pobox.com>
> Jeremy>   Also, because nobody seems to warn others of this: if
> Jeremy> you go the ZFS route on FreeBSD, please do not use
> Jeremy> features like dedup or compression.
> 
> While dedup is memory and sometimes cpu hungry, so HW spec
> should be considered before using it, compression is not so
> and I've not seen any valid reason not to use it should it
> fit your uses.
> 
> We actually use compression extensivily here and we've
> had nothing but positive results from it so sounds like
> FUD to me.

The problem with the lack of separate and prioritised write threads for
dedup and compression, thus causing interactivity stalls, is not FUD,
it's fact.  I explained this in the part of my reply to Berend which you
omitted, which included the proof and acknowledgement from folks who
are in-the-know (Bob Friesenhahn).  :/  Nobody has told me "yeah that
got fixed", so there is no reason for me to believe anything has
changed.

If a person considering use of compression on FreeBSD ZFS doesn't mind
that problem, then by all means use it.  It doesn't change the fact that
there's an issue, and one that folks should be made aware of up front.
It's not spreading FUD: it's spreading knowledge of a certain behaviour
that differs between FreeBSD and Solaris/Illumos.  The issue is a
deal-breaker for me; if it's not for you, great.

-- 
| Jeremy Chadwick                                   jdc at koitsu.org |
| UNIX Systems Administrator                http://jdc.koitsu.org/ |
| Making life hard for others since 1977.             PGP 4BD6C0CB |