Re: [9fans] threads vs forks

["J.R. Mauro" <jrm8005@gmail.com>]

On Wed, Mar 4, 2009 at 12:14 PM, ron minnich <rminnich@gmail.com> wrote:
> On Wed, Mar 4, 2009 at 8:52 AM, J.R. Mauro <jrm8005@gmail.com> wrote:
>
>> Now I haven't tested an SSD for performance, but I know they are
>> better.
>
> Well that I don't understand at all. Is this "faith-based" performance
> measurement? :-)

No, I have seen several benchmarks. The benchmarks I haven't seen are
ones for "how long does it take to actually break these drives?" from
anyone other than the manufacturer.

>
> I have a friend who is doing lots of SSD testing and they're not
> always better. For some cases, you pay a whole lot more for 2x greater
> throughput.
>
> it's not as simple as "know they are better".

What types of things degrade their performance? I'm interested in
seeing other data than the handful of benchmarks I've seen. I imagine
writes would be the culprit since you have to erase a whole block
first?

>
>>If I got one, this problem would likely subside, but I'm not
>> convinced that SSDs are durable enough, despite what the manufacturers
>> say. I haven't seen many torture tests on them, but the fact that
>> erasing a block destroys it a little bit is scary. I do a lot of
>> sustained writes with my typical desktop workload over the same files,
>> and I'd rather not trust them to something that is delicate enough to
>> need filesystem algorithms to be optimized for so they don't "wear
>> out".
>
> in most cases write leveling is not in the file system. It's in the
> hardware or in a powerpc that is in the SSD controller.  It's worth
> your doing some reading here.

I've seen a lot about optimizing the next-generation filesystems for
flash. Despite the claims that the hardware-based solutions will be
satisfactory, there are a lot of people interested in making existing
filesystems smarter about SSDs, both for wear and for optimizing
read/write.

Beyond that, though, I feel very shaky just hearing the term "wear
leveling". I've had more flash-based devices fail on me than hard
drives, but maybe I'm just crazy and the technology has gotten decent
enough in the past couple years to allay my worrying. It would just be
nice to see a bit stronger alternative being pushed as hard as SSDs.

>
> That said, I sure would like to have a fusion IO card for venti. From
> what my friend is telling me the fusion card would be ideal for venti
> -- as long as we keep only the arenas  on it.
>
> ron
>
>