From: Craig Ringer <craig@postnewspapers.com.au>
To: Andy <angelflow@yahoo.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: BBU still needed with SSD?
Date: Mon, 18 Jul 2011 10:30:20 +0800
Message-ID: <4E239ABC.4020204@postnewspapers.com.au> (raw)
In-Reply-To: <1310953399.25726.YahooMailClassic@web111304.mail.gq1.yahoo.com>
References: <1310953399.25726.YahooMailClassic@web111304.mail.gq1.yahoo.com>
On 18/07/2011 9:43 AM, Andy wrote:
> Hi,
>
> Is BBU still needed with SSD?
You *need* an SSD with a supercapacitor or on-board battery backup for
its cache. Otherwise you *will* lose data.
Consumer SSDs are like a hard disk attached to a RAID controller with
write-back caching enabled and no BBU. In other words: designed to eat
your data.
> In this case is BBU still needed? If I put 2 SSD in software RAID 1, would that be any slower than 2 SSD in HW RAID 1 with BBU? What are the pros and cons?
>
You don't need write-back caching for fsync() performance if your SSDs
have big enough caches. I don't know enough to say whether there are
other benefits to having them on a BBU HW raid controller or whether SW
RAID is fine.
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To: pgsql-performance@postgresql.org
Cc: craig@postnewspapers.com.au, angelflow@yahoo.com
Subject: Re: BBU still needed with SSD?
In-Reply-To: <4E239ABC.4020204@postnewspapers.com.au>
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