From: Bruce Momjian <bruce@momjian.us>
To: Graeme B. Bell <grb@skogoglandskap.no>
Cc: pgsql-admin@postgresql.org <pgsql-admin@postgresql.org>
Subject: Re: raid writethrough mode (WT), ssds and your DB. (was Performances issues with SSD volume ?)
Date: Thu, 28 May 2015 10:27:13 -0400
Message-ID: <20150528142713.GA18209@momjian.us> (raw)
In-Reply-To: <5F6C17BC-7487-4E24-B322-39FEC6373C92@skogoglandskap.no>
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On Thu, May 28, 2015 at 01:37:48PM +0000, Graeme B. Bell wrote:
> Hi Bruce
>
> I'm *extremely* certain of what I say when I say WB+BBU=good and direct WT=bad.
It is my understanding that write-through is always safe as it writes
through to the layer below and waits for acnoledgement. Write-back
doesn't, so when you say:
> WT should be OK with e.g. Intel SSDs.
I assume you mean Write-Back is OK because the drive has a BBU, while
Write-Through is always safe.
You also say:
> >> - WT with most SSDs will likely corrupt your postgres database the
> >> first time you lose power. (on all the drives I've tested)
which contradicts what you said above, and I assume you mean write-back
here.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
--
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To: pgsql-admin@postgresql.org
Cc: bruce@momjian.us, grb@skogoglandskap.no
Subject: Re: raid writethrough mode (WT), ssds and your DB. (was Performances issues with SSD volume ?)
In-Reply-To: <20150528142713.GA18209@momjian.us>
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