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From: "A.M." <agentm@themactionfaction.com>
Subject: Re: Making the most of memory?
Date: Wed, 23 Jan 2008 15:40:28 -0500
To: pgsql-performance@postgresql.org


On Jan 23, 2008, at 2:57 PM, Guy Rouillier wrote:

> Scott Marlowe wrote:
>> I assume you're talking about solid state drives?  They have their
>> uses, but for most use cases, having plenty of RAM in your server  
>> will
>> be a better way to spend your money.  For certain high throughput,
>> relatively small databases (i.e. transactional work) the SSD can be
>> quite useful.
>
> Unless somebody has changes some physics recently, I'm not  
> understanding the recent discussions of SSD in the general press.   
> Flash has a limited number of writes before it becomes unreliable.   
> On good quality consumer grade, that's about 300,000 writes, while  
> on industrial grade it's about 10 times that.  That's fine for mp3  
> players and cameras; even professional photographers probably won't  
> rewrite the same spot on a flash card that many times in a  
> lifetime.  But for database applications, 300,000 writes is  
> trivial. 3 million will go a lot longer, but in non-archival  
> applications, I imagine even that mark won't take but a year or two  
> to surpass.

Please let outdated numbers rest in peace.
http://www.storagesearch.com/ssdmyths-endurance.html

Conclusion:
"With current technologies write endurance is not a factor you should  
be worrying about when deploying flash SSDs for server acceleration  
applications - even in a university or other analytics intensive  
environment. "

That said, postgresql is likely making assumptions about non-volatile  
storage that will need to be shattered once SSDs become more widely  
deployed. Perhaps SSDs will replace RAID BBUs and then the HDs  
themselves?

Cheers,
M