[AccessD] SSD - Anything to it?

Rocky,

 >Seems to me that response time is largely data transfer to and from the disk - so in that case you 
wouldn't see any difference. A query that takes 20 seconds would still take twenty seconds, no?

It is way more than that.

The point of an SSD is:

1) They can transfer data faster, i.e. they can read blocks of data and transfer those blocks at 
electronic speeds.
2) They can access a specific sector faster.  With rotating media, you have to position the head (9 
milliseconds or so) and then wait for the disk to rotate the desired data under the head (~1-2 ms 
depending on rotation speed).  Only then can the data actually stream off the disk.  This is known 
as "Access time" with rotating media.
3) The data streaming out of the read head is limited to the speed of the data coming off the 
rotating disk.  With modern disks with vertical recording (on the magnetic media) this is quite 
high.  The old linear encoding is not very high.  In any case the data tends to stream off the 
current fastest disk about 60 to 100 megabytes / second (once found - see 2 above)

So, what you have is a situation where, with rotating media, you cannot get more than 100-200 "IOPS" 
(I/O operations / second).  IOW the head cannot move back and forth between tracks more than 100-200 
times per second MAXIMUM.  If it is trying to do that from inner track to outer track, it will be 
even less than that.

All of that stuff goes away with SSDs.  There is no head, so the "Access time" drops to a fixed 
value, the same all of the time.  It averages somewhere around .1 millisecond to "access the data" 
or get the data started streaming off the disk to the computer.  That is .1 millisecond vs 8-12 
milliseconds or about 100 times faster, just to access the data.

The data reading out of the memory chips is also faster, and can be as high as 200-250 megabytes 
streaming reads.

Between the two factors, SSDs can routinely perform anywhere from 2000 to 50,000 IOPS.  IOW they can 
access 10,000 (pulled out of thin air from somewhere between these two figures) DIFFERENT sets of 
data in a second vs 100-200 for rotating media.

This does NOT translate to 100-1000 times faster queries (or anything else), because you will hit a 
bottleneck somewhere else in the system.  What it means is that the disks will no longer be slowing 
down the loading of the query data into memory, i.e. the computer will not be waiting for the disks 
any more.

This seems to be pretty true.

John W. Colby
www.ColbyConsulting.com

On 10/12/2010 9:34 AM, Rocky Smolin wrote:
> Do you use it as Kingston was saying - put the OS and apps on it?  Do you
> notice any improvement in response time.  Seems to me that response time is
> largely data transfer to and from the disk - so in that case you wouldn't
> see any difference. A query that takes 20 seconds would still take twenty
> seconds, no?
>
> R
>
>
> -----Original Message-----
> From: accessd-bounces at databaseadvisors.com
> [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of jwcolby
> Sent: Tuesday, October 12, 2010 5:59 AM
> To: Access Developers discussion and problem solving
> Subject: Re: [AccessD] SSD - Anything to it?
>
> Rocky,
>
> I cannot discuss any specific brand other than the one I use, but I can say
> that SSDs in general *rock*, with the right supports.
>
> They are not drop in replacements yet - your grandma probably wouldn't
> wanna.  There are trim issues and firmware update issues but things are
> getting better.
>
> John W. Colby
> www.ColbyConsulting.com
>
> On 10/11/2010 6:26 PM, Rocky Smolin wrote:
>> http://www.youtube.com/kingstonssdnow
>>
>> Maybe you could win one:
>>
>> http://www.kingston.com/ssd/destructo/default.asp
>>
>>
>>
>> Rocky
>>
>>
>>
>>
>>
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