Re: Hardware recommendations

If you are worried about wearing out the SSD's long term get a larger SSD and create the partition smaller than the
disk,this will reduce the write amplification and extend the life of the drive.
 

TRIM support also helps lower write amplification issues by not requiring as many pages to do the writes, and improve
performanceas well!
 

As a test I bought 4 cheap 40GB drives in a raid0 software stripe, I have run it for almost a year now with a lot of
randomIO.  I portioned them as 30GB drives, leaving an extra 25% spare area to reduce the write amplification, I can
stillget over 600MB/sec on these for a whopping cost of $400 and a little of my time.
 

SSD's can be very useful, but you have to be aware of the shortcomings and how to overcome them.

- John

-----Original Message-----
From: Marti Raudsepp [mailto:marti@juffo.org] 
Sent: Thursday, December 09, 2010 6:09 AM
To: Scott Marlowe
Cc: Benjamin Krajmalnik; John W Strange; pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Hardware recommendations

On Thu, Dec 9, 2010 at 04:28, Scott Marlowe <scott.marlowe@gmail.com> wrote:
> On Wed, Dec 8, 2010 at 5:03 PM, Benjamin Krajmalnik <kraj@servoyant.com> wrote:
>> My biggest concern with SSD drives is their life expectancy,
>
> Generally that's not a big issue, especially as the SSDs get larger.
> Being able to survive a power loss without corruption is more of an
> issue, so if you go SSD get ones with a supercapacitor that can write
> out the data before power down.

I agree with Benjamin here. Even if you put multiple SSD drives into a
RAID array, all the drives get approximately the same write load and
thus will likely wear out and fail at the same time!

> As for the Areca controllers, I haven't tested them with the latest
> drivers or firmware, but we would routinely get 180 to 460 days of
> uptime between lockups

That sucks! But does a BBU even help with SSDs? The flash eraseblock
is larger than the RAID cache unit size anyway, so as far as I can
tell, it might not save you in the case of a power loss.

Any thoughts whether software RAID on SSD is a good idea?

Regards,
Marti

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