[oi-dev] SSD-based pools

[Schweiss, Chip]

On Mon, Sep 29, 2014 at 2:06 PM, Andrew M. Hettinger <
AHettinger at prominic.net> wrote:

> "Schweiss, Chip" <chip at innovates.com> wrote on 09/28/2014 10:07:15 AM:
>
> >
> > I would suspect hardware.   Avoid overly cheap SAS cables.
>
> I'll try it in another machine as soon as I can, but it seems to work fine
> with spinning HDs.
>
>
> > I also always run SAS to SATA interposers to keep the SAS buses
> > happy.    However, Samsung SSDs are the only brand SSD that I found
> > to consistently work with the interposers.
>
> Can you link me to the interposers? I wonder if that would make a
> difference.
>
> I run the Supermicro / LSI Interposers.  AOC-SMP-LSISS9252  I purchase
them from GovConnection (PC Connection)

http://www.govconnection.com/shop/supermicro-lsi-interposer-card/10774712?cac=Result


> >
> > All my HBAs are LSI 2308 and 2008 controller based.   Make sure your
> > firmware is up to date.  There have been many SSD related fixes in
> > the LSI HBA.
>
> Firmware is current. I checked LSI's site last week.
>
> > If you can avoid it don't use a SAS expander, they will slow things
> > down and without interposers are susceptible to reset storms.
>
> There is no SAS expanders involved.
>
> > A log device is really necessary on an SSD pool.   The sync write
> > behavior of ZFS simply does not work well with SSDs with out a log.
> >   Using an 850 is not a good choice for a log device because it does
> > not have power loss protections. You are better off turning sync off
> > than trying to use them as a log.
>
> Can you make a recommendation for the slog?
>

I run the ZeusRAM on my production SSD pool with sTec ZeusIOPS SAS SSDs.
I've heard good results from the Intel DC S3700 working well as log, but
they are also SATA and would not work with an interposer for me.

On my scratch pool with the 840 Pros, I turn sync off.   The 840 Pro and
I'm assuming the 850 alike does a cache flush on on sync writes and
performance hits the floor, so if you care about the data and the
performance, proper log is necessary.

And in case anyone is wondering, no I don't care about the data on the
scratch pool, its always transient and reproducible.  Performance is the
objective.  ZFS will tell me if it is incorrect and I will know it needs
regenerated.

-Chip

>
> >
> > -Chip
>
> Thanks for everyone's help here!
>
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