| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | "Graeme B(dot) Bell" <grb(at)skogoglandskap(dot)no> |
| Cc: | "pgsql-admin(at)postgresql(dot)org" <pgsql-admin(at)postgresql(dot)org> |
| Subject: | Re: raid writethrough mode (WT), ssds and your DB. (was Performances issues with SSD volume ?) |
| Date: | 2015-05-28 14:27:13 |
| Message-ID: | 20150528142713.GA18209@momjian.us |
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| Thread: | |
| Lists: | pgsql-admin |
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(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
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