[mythtv-users] SSDs and Myth frontends ?

Daniel Kristjansson danielk at cuymedia.net
Sat Sep 18 01:06:44 UTC 2010


On Thu, 2010-09-16 at 18:22 -0600, Brian Wood wrote:
> Someone just gave me a 64GB SSD (probably buttering me up for some other favor in the future, like building him a Myth 
> system).
> 
> I was thinking about replacing the 2.5" HDD that came with my Revo with it.
I would not.. read on.

> I don't really see any advantage, other than power consumption, heat and reliability.
It really depends on the unit, unfortunately some SSD's produce
a lot of heat and consume more power than the HDD's they replace.

> But I have read a few things about the net about SSDs causing long pauses,
<snip>
> If it matters, it's a (relatively) cheap Kingston unit, I've seen them
> around for $120. I know Linus says to not buy anything but an Intel SSD,
> but he probably has more money than I do, and may get hardware for free.

It matters. You may get better advice if you report the model number
or the unit; but in general a lot of the cheaper units tend to have
horrendous write latency:
  unit      avg latency  max latency
  OCZ Core    250  ms     990 ms
  Intel X25-M 0.09 ms      94 ms

Your average 3.5" hard drive will have avg 9 ms and max 75 ms. Most
2.5" HDD will be a bit slower, but there are of course some that
are actually faster since the heads move less than in 3.5" HDD's.

These numbers are per random 4KB write, with much larger writes
the HDD's really shine because it's the seeks that really hurt
their performance.

OCZ does make faster drives some of which I might even recommend*,
but the SSD drives on the lower end of the price spectrum should be
treated like EEPROM. Stick /usr/ on there so your apps can load
quickly, but not /home and especially not /var or /tmp. If a write
is scheduled and it becomes one of those 1 second writes then all
reads and writes from any application are suspended while that one
write is being processed.

The low end SSD's aren't useless, but you can see from the numbers
that they are far from ideal for things that get written to disk
often, like the system logs and DB's in /var and the app data stores
in /home, the scratch files in /tmp, etc.

I really don't know if this applies to your Kingston drive though.
They have sold SSD's with Intel's controller, as well as other
lesser controllers.

* This is slightly unfair to OCZ because they now have the Solid2
  line of budget drives with much better performance.

-- Daniel



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