[mythtv-users] MySQL on SSD 99% Utilization

[R. G. Newbury]

On 02/03/2011 01:38 PM, Matthew McClement wrote:
> On 02/03/2011 05:43 PM, Raymond Wagner wrote:
>> On 2/3/2011 12:37, Matthew McClement wrote:
>>> On 02/03/2011 05:27 PM, Raymond Wagner wrote:
>>>> On 2/3/2011 11:40, Brian Long wrote:
>>>>> The CPUs are doing almost nothing so it appears the MySQL updates
>>>>> being performed during a commflag are screwing with the SSD.  Is it
>>>>> generally a bad practice to put MySQL on a SSD?  I figured it would
>>>>> provide a nice fast DB and keep my DB separate from my recording
>>>>> disks, but I guess I was wrong.
>>>> Looking at reviews on the SSDNow V 30GB, the one thing that stands out
>>>> is awful random read/write performance.  Even still, it should be far
>>>> better than a disk drive is capable of.
>>> Anands benchmarks show the SSDNow V 30GB is the same speed as a
>>> Velociraptor at 4K random writes, which is pretty terrible for a SSD:
>>>
>>> http://www.anandtech.com/bench/Product/155?vs=182
>>
>> That metric just looks wrong.  It looks like they're buffering writes to
>> something other than the drive, and that something else is actually what
>> is bottlenecking.  That's the only way to account for the discrepancy
>> between reads and writes.  Measuring write buffer speed is meaningless
>> unless that write buffer is battery backed and recoverable.
>
> Eh? SSD's are significantly slower at writes than reads, especially if
> you're writing to a non-GC'd cell, which with how the Toshiba controller
> handles TRIM is entirely possible(GC isn't continuous but rather seems
> to be demand triggered). If you then add non-aligned sub-page sized
> writes, things can get bad pretty quickly.
>
> It's buffering and other tricks which make SSD's faster today over the
> early versions, rather than slower.
>
> And it's not like that result is an oddity. Just look at any benchmark
> for the early JMicron based SSDs to see SSDs that were often *slower*
> than hard disks at random writes.
>
> Matt


There are an interesting exposition and drive test statistics here, 
concerning the problem with slow IOPs (writes) on SSD's. The tech 
referred to there is supposed to be awesome. ( Ihaven't tried it).

http://easyco.com/mft/understanding/fastest.htm

Geoff