[dba-Tech] SSD Diagnoser

[John Colby]

Jim,

As I repeat I am not an "expert", but your are in a way correct. SSDs 
have a /dedicated/ section of memory (the disk) used for repairing the 
disk, and yes, the more expensive the SSD the larger this section.  Thus 
if the disk is completely full, then the more expensive disk can "self 
repair" longer because of this larger dedicated area.  However, if the 
disk is not completely full, then the controller can simply move data 
out of sectors which are dying into other sectors which are fine and map 
the bad sectors, in the same manner that a rotating disk will do.

As I used in my example, suppose I have an MDB file which gets written 
to a lot, and a huge PDF file which is written once and just sits 
there.  (As I understand it) the controller will figure out that the MDB 
file is "wearing out" the sectors it sits in, and can simply "swap" the 
MDB file with PDF file.  The memory cells that the PDF has been sitting 
in are absolutely brand new, written once.

You can see how this concept can "level" the wear of the disk, even 
without dipping into the dedicated areas used just for such "repair".

SSDs are actually rated in total Terabytes written, and / or Gigabytes / 
day written.  As I visualize it, the disk is essentially "used up" 
(eventually) as the wear leveling algorithms moves high wear files into 
low wear areas.  Modern SSDs are pretty much not going to wear out 
unless you are using them for high transaction databases or something 
like that.  IOW on the desktop they will probably never wear out.

On 9/8/2016 10:48 PM, Jim Lawrence wrote:
> I believe you are correct...sort of self-healing drives. But as I understand it there is a limit to how much a drive can self-repair...the more expensive the SSD the greater the limit.
>
> Jim
>
> ----- Original Message -----
> From: "John Colby" <jwcolby at gmail.com>
> To: "Discussion of Hardware and Software issues" <dba-tech at databaseadvisors.com>, jwcolby at gmail.com
> Sent: Tuesday, September 6, 2016 4:25:45 PM
> Subject: Re: [dba-Tech] SSD Diagnoser
>
> I have heard (can't swear to it) that even if there is a bad spot, the
> SSD internal controller will find it before it is completely
> non-functional, then move the data and mark the spot (sectors) bad.
>
> So if you have a completely full (or very near full) drive, you may
> eventually have a real problem.  If not, then the unused areas will be
> used to hold the moved data if necessary.  I have also read that the
> SSDs have "wear leveling" algorithms which will spread the writes
> around.  Only writes are damaging to the SSDs.
>
> If you think about it, any given cell can be written to about 2000
> times.  Most of a drive is used to store files.  Most files are written
> once and then sit there (unmoving) for the next 10 years. There are
> specific areas that get changed a lot (think an MDB file, or a swap
> file) but they are really few and far between.
>
> One thing you do not want to do is run a defragger though.  Why? The SSD
> does not have to move heads so it is (almost) as fast to read fragments
> spread all over hell as it is to read a nice linear file.  And... the
> defragger reads that file that otherwise would not move for the next 10
> years and moves it intentionally to try and get it in fewer fragments.
> So the defragger causes wear that meant nothing in a rotating disk but
> which means a lot (or more anyway) in an SSD.
>
> I can tell you that I have used SSDs in a raid 6 controller with active
> database usage for many MANY years and never had an issue.
>
> As to your question, I have never seen a program which will "show you"
> wear happening on the SSD.
>
> On 9/6/2016 10:51 AM, Rocky Smolin wrote:
>> Dear List:
>>
>>    
>>
>> I upgraded my comp to an SSD about a year ago.  I've hears that they don't
>> last forever and develop bad spots over time. I'm curious to know how this
>> one is doing and to have a tool to monitor it from time to tie.
>>
>>    
>>
>> Any recommendations?
>>
>>    
>>
>> MTIA
>>
>>    
>>
>>    
>>
>> Rocky Smolin
>>
>> Beach Access Software
>>
>> 760-683-5777
>>
>>    <http://www.bchacc.com> www.bchacc.com
>>
>>    <http://www.e-z-mrp.com> www.e-z-mrp.com
>>
>> Skype: rocky.smolin
>>
>>    
>>
>>    
>>
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>> .
>>

-- 
John W. Colby