Message-ID: <4E23E72B.2070508@gmail.com>
Date: Mon, 18 Jul 2011 09:56:27 +0200
From: Yeb Havinga <yebhavinga@gmail.com>
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To: Andy <angelflow@yahoo.com>
CC: pgsql-performance@postgresql.org
Subject: Re: BBU still needed with SSD?
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On 2011-07-18 03:43, Andy wrote:
> Hi,
>
> Is BBU still needed with SSD?
>
> SSD has its own cache. And in certain models such as Intel 320 that cache is backed by capacitors. So in a sense that cache acts as a BBU that's backed by capacitors instead of batteries.
>
> In this case is BBU still needed? If I put 2 SSD
+with supercap?
>   in software RAID 1, would that be any slower than 2 SSD in HW RAID 1 with BBU? What are the pros and cons?
The biggest drawback of 2 SSD's with supercap in hardware raid 1, is 
that if they are both new and of the same model/firmware, they'd 
probably reach the end of their write cycles at the same time, thereby 
failing simultaneously. You'd have to start with two SSD's with 
different remaining life left in the software raid setup.

regards,
Yeb