Message-ID: <5140DE90.5010009@boreham.org>
Date: Wed, 13 Mar 2013 14:16:16 -0600
From: David Boreham <david_list@boreham.org>
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To: pgsql-performance@postgresql.org
Subject: Re: New server setup
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On 3/13/2013 1:23 PM, Steve Crawford wrote:
>
> What concerns me more than wear is this:
>
> InfoWorld Article:
> http://www.infoworld.com/t/solid-state-drives/test-your-ssds-or-risk-massive-data-loss-researchers-warn-213715 
>
>
> Referenced research paper:
> https://www.usenix.org/conference/fast13/understanding-robustness-ssds-under-power-fault 
>
>
> Kind of messes with the "D" in ACID.

It is somewhat surprising to discover that many SSD products are not 
durable under sudden power loss (what where they thinking!?, and ...why 
doesn't anyone care??).

However, there is a set of SSD types known to be designed to address 
power loss events that have been tested by contributors to this list.
Use only those devices and you won't see this problem. SSDs do have a 
wear-out mechanism but wear can be monitored and devices replaced in 
advance of failure. In practice longevity is such that most machines 
will be in the dumpster long before the SSD wears out. We've had 
machines running with several hundred wps constantly for 18 months using 
Intel 710 drives and the wear level SMART value is still zero.

In addition, like any electronics module (CPU, memory, NIC), an SSD can 
fail so you do need to arrange for valuable data to be replicated.
As with old school disk drives, firmware bugs are a concern so you might 
want to consider what would happen if all the drives of a particular 
type all decided to quit working at the same second in time (I've only 
seen this happen myself with magnetic drives, but in theory it could 
happen with SSD).


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