[mythtv-users] my experience with myth on a solid state drive

[Steven Adeff]

On Thu, Jan 5, 2012 at 1:26 PM, Robert Longbottom
<rongblor at googlemail.com> wrote:
> On 05/01/2012 16:20, Ronald Frazier wrote:
>> A few months ago, I got a new larger SSD drive for my desktop
>> computer, to replace the older, smaller SSD I had previously (a 1st
>> generation Intel 80GB). I then decided to take that old drive and use
>> that as the primary drive for my myth system. Wow, what an incredible
>> performance boost it has been.
>
> I did a similar thing about 9 months ago and bought an SSD for my myth
> backend / server and I agree.  It's one of the best performance
> improvements you can make at the moment.
>
>> Before I made the switch, I did a lot of reading about SSD drives in
>> linux, and people talking about putting /tmp or /var or this or that
>> onto a physical drive or a tmpfs. The reasoning for all of this is
>> that SSDs wear out from excessive writing (unlike HDDs). I figured I'd
>> ignore all of that advice and just give it a shot with everything all
>> on the SSD (except for my recordings/movies, of course). The only
>> thing particular I did was to pay attention to partition
>> alignment...some resources said to align it to 512K boundaries, other
>> said 1MB boundaries. I played it safe and aligned it to 1MB.
>
> I too have taken the approach of just dump it all on the SDD and not
> worry about wear leveling, etc too much on the basis that by the time my
> SSD wears out they will be dirt cheap and I can just replace it.
>
>> The intel drives are rated for at least 5 years of 20GB/day of writes.
>> You can check the current wear level using the SMART feature of the
>> drive. After using this drive in my Windows box for over 3 years, the
>> drive still had 93% of it's rated life remaining, so I should have at
>> least 4 years of life at 20GB/day. So I began running my system and
>> periodically monitoring the wear level. Immediately I discovered I was
>> writing about 30+GB/day, which meant the drive would only last about 3
>> years. So off I went trying to figure out what was doing so much
>> writing. Was it mysql, or logging, or the fact that I'm also running
>> my 2 frontend systems (which are diskless boots) from this drive, or
>> /tmp? So I began systematically moving things one by one to another
>> partition, watching it for a few days, and then moving back when I saw
>> no change. Finally when I got to moving /tmp, that made all the
>> difference. SSD writes dropped down to about 2GB/day, which means it
>> would take 40 years to use up the drive's rated write life.
>>
>> So what was doing all the writes to /tmp? Several times an hour, myth
>> recalculates its schedule. When it does, it uses about 500MB of
>> temporary mysql tables. That alone was responsible for over 90% of the
>> writes on the SSD. So instead, I created /tmp as a tmpfs partition.
>> I've got 2GB of ram, so that gives /tmp up to 1GB to use.
>>
>> So far that's worked just fine with just that one change. I never had
>> to mess with all of the other things people say to do to minimize
>> wear, like alter the io scheduler or the cache flush timings, or move
>> /var or /var/log.
>
> Thats interesting.  How exactly are you montoring wear level and the
> amount of data being written to your SSD?  Is it specific to the Intel
> ones? - mine is a Kingston I think
>
> Sounds like I might need to think about switching mysql temp tables to
> ram rather than SSD as well if it's a simple change.
>
> Cheers,
> Robert.

until I can move to an SSD, I will at least take advantage of using
tmpfs for my /tmp
dunno if it will make much difference, but it seems like unnecessary
HDD writes either way.

now to keep an eye out for a small, fast, cheap SSD drive. I wonder if
there are any PATA SSD drives?


-- 
Steve
http://www.mythtv.org/wiki/User:Steveadeff
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