From: Karl Denninger <karl@denninger.net>
To: Steve Crawford <scrawford@pinpointresearch.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: New server setup
Date: Wed, 13 Mar 2013 14:38:27 -0500
Message-ID: <5140D5B3.7080104@denninger.net> (raw)
In-Reply-To: <5140D226.4060609@pinpointresearch.com>
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On 3/13/2013 2:23 PM, Steve Crawford wrote:
> On 03/13/2013 09:15 AM, John Lister wrote:
>> On 13/03/2013 15:50, Greg Jaskiewicz wrote:
>>> SSDs have much shorter life then spinning drives, so what do you do
>>> when one inevitably fails in your system ?
>> Define much shorter? I accept they have a limited no of writes, but
>> that depends on load. You can actively monitor the drives "health"
>> level...
>
> 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-w...
>
>
> Referenced research paper:
> https://www.usenix.org/conference/fast13/understanding-robustness-ssds-under-power-fault
>
>
> Kind of messes with the "D" in ACID.
>
> Cheers,
> Steve
One potential way around this is to run ZFS as the underlying filesystem
and use the SSDs as cache drives. If they lose data due to a power
problem it is non-destructive.
Short of that you cannot use a SSD on a machine where silent corruption
is unacceptable UNLESS you know it has a supercap or similar IN THE DISK
that guarantees that on-drive cache can be flushed in the event of a
power failure. A battery-backed controller cache DOES NOTHING to
alleviate this risk. If you violate this rule and the power goes off
you must EXPECT silent and possibly-catastrophic data corruption.
Only a few (and they're expensive!) SSD drives have said protection. If
yours does not the only SAFE option is as I described up above using
them as ZFS cache devices.
--
-- Karl Denninger
/The Market Ticker ®/ <http://market-ticker.org;
Cuda Systems LLC
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To: pgsql-performance@postgresql.org
Cc: karl@denninger.net, scrawford@pinpointresearch.com
Subject: Re: New server setup
In-Reply-To: <5140D5B3.7080104@denninger.net>
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