[OpenIndiana-discuss] SSDs honoring cache flush?

[Robbie Crash]

I thought there were perfomance issues with using SLOGs in general on OI
since 148?

On Tue, Apr 24, 2012 at 16:11, Richard Elling <
richard.elling at richardelling.com> wrote:

> On Apr 24, 2012, at 12:35 PM, Roy Sigurd Karlsbakk wrote:
>
> > Hi all
> >
> > There was a discussion some time back about some (or most?) SSDs not
> honoring cache flushes, that is, something is written to, say, the SLOG,
> and ZFS sends a flush(), the SSD issues a NOP and falsely acknowledges the
> flush.
>
> Some people accused SSD vendors of not honoring cache flush. IIRC, the
> allegations were not proven.
>
> >
> > Now, I've gotten an offer for an SSD that looks good for SLOG, OCZ
> Deneva 2 C SLC 30GB 2.5" SSD. This does not have supercap, but so long as
> it honors cache flush, then it won't make a huge difference, since if a
> write() happens, the SSD cache is flushed to the SSD media, this probably
> won't take more than a handful of milliseconds, and the difference between
> that and backing up the cache, seems minimal.
>
> I've known people to use that SSD without issue.
>
> Here is an article that sheds a little bit of light on the various SSD
> designs. Unfortunately, it does not address the issue that HDDs have
> with their volatile caches and why cache flush commands are so important.
>
> http://www.storagesearch.com/ssd-power-going-down.html
>
>  -- richard
>
> --
> ZFS Performance and Training
> Richard.Elling at RichardElling.com
> +1-760-896-4422
>
>
>
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