[mythtv-users] Anyone using SSD for long term storage?

Warpme warpme at o2.pl
Thu Jul 24 20:20:41 UTC 2014


On 24/07/14 17:04, Thomas Mashos wrote:
> On Thu, Jul 24, 2014 at 2:16 AM, Warpme <warpme at o2.pl> wrote:
>> On 23/07/14 23:26, Joseph Fry wrote:
>>
>>> On Wed, Jul 23, 2014 at 2:49 PM, jacek burghardt
>>> <jaceksburghardt at gmail.com <mailto:jaceksburghardt at gmail.com>> wrote:
>>>
>>>      Well do you guys think that using ssd for buffer will imrove mythtv ?
>>>
>>>
>>> Define improve.
>>>
>>> Unlike others, I like the idea of using an SSD as a recording drive...
>>> because of the lack of access times I could easily sustain all of my
>>> recordings and playback on a single drive... i currently use 3 spinning
>>> recording disks.
>> .....
>>
>>> Note, I tried recording 5 HD streams to a single spinning disk, and while
>>> it seemed to work, I could hear the drive thrashing.  Spreading the
>>> recordings over 3 smaller drives made a huge difference, especially because
>>> I have peaked at 8 HD recordings at once.
>> Honestly I don't see point to make things more complicated than required.
>> Adding additional drives because "I could hear the drive thrashing" seems to
>> be little surprising for me.
>> Using latter jobqueue to reshuffle recordings....oh my Dear - I understand
>> setup of this was nice brain training during those winter evenings :-)
>> MythTV is pretty effective with multiple sustained writes to storage. I done
>> many tests with 16xHD in single HDD (WD Green 3TB) - no any problem. Sure -
>> HDD LED was constant ON. But HDD role is write/read - so as long as IO wait
>> is reasonable - I don't see issue.
>>
>>> For the database, you can see a substantial improvement unless your mysql
>>> configuration is heavily optimized to eliminate disk reads.
>> This is interesting.
>> Pls look here
>> http://www.gossamer-threads.com/lists/mythtv/users/519664#519664
>>
>> Exec summary from above link:
>>
>> 1.In case of my system build-in-kernel disk buffering is so effective
>> that even significant speedup of next level storage hierarchy (HDD->SSD)
>> is totally masked by kernel buffering.
>>
>> 2.Big enough MySQL caches quite effectively masks speedups in mass-storage.
>>
>> 3.Recordings rescheduling speed is directly correlated to CPU (going
>> from Celeron 3,46G to AMD 235E changed reschedule time from 60s to 18s).
>>
>> 4.For rescheduling speed-up, next, after CPU upgrade & mysql caches, is
>> moving /tmp to tempfs (noticeable speedup 18s->6s).
>>
>> 5.Current MythTV system based on quite standard HDD like WD Green is
>> working really nice even with ATOM CPU. (i.e.86 progs EPG list loads in
>> aprox 0.2-0.4sec; showing 400+ recordings list is instant (in sense that
>> there is no time to show loading progress dialog).
>>
>> Summarizing:
>> Speaking in economy: HDD->SSD marginal utility increase is in my case
>> was ABSOLUTELY not worth of SSD investment.
>>
>> Before SSD spending decision I'm strongly recommending:
>>
>> -buy more RAM for having huge as possible kernel disk buffers
>> -move /tmp to tempfs
>> -allocate 32MB or more for MySQL query cache (and other parameters
>> accordingly to http://mysqltuner.pl/)
>>
>> With above it is highly probable that You will get MythTV system where
>> HDD->SSD upgrade will absolutely not worth the money (and allows You
>> spent those money elsewhere - with much higher utility).
>>
>> YMMV
>>
>>
>> _______________________________________________
> While I agree with most of what you said, I do find it a bit humorous
> that you're discussing putting the MySQL DB onto an SSD as some kind
> of huge investment. We're talking under $50 here. Would RAM be faster?
> Yes, but it's also more expensive.
>
> Everything has it's trade-offs I suppose
>
> Thanks,
>
> Thomas Mashos
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>
Right :-)
It was 2y ago and at that time I spent equivalent of 16GB of RAM for 
Samsung 840 model.
Purchase decision was exactly because many ppl said "I move to SSD and 
difference is night-to-day".
What was my surprise when I discover practically zero of subjective 
speed-up....
Next it was confirmed by some quantitative analysis.
I really miss those 16GB alternative :-(
OTOH my experience is proof how well current kernels are dealing with 
caching/buffering for mythtv-like workloads.








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