public inbox for [email protected]
help / color / mirror / Atom feedFrom: Merlin Moncure <[email protected]>
To: Scott Marlowe <[email protected]>
Cc: Kaixi Luo <[email protected]>
Cc: postgres performance list <[email protected]>
Subject: Re: Tuning guidelines for server with 256GB of RAM and SSDs?
Date: Thu, 7 Jul 2016 11:27:10 -0500
Message-ID: <CAHyXU0zKE29Uu2_Bq_6O2pUhGLVn8Xs4SLNpSa8gR1z5mOei1A@mail.gmail.com> (raw)
In-Reply-To: <CAOR=d=13st6GcimEaMD-mMftBkeB7fhhgPWop-CASpFGyHyOaw@mail.gmail.com>
References: <CAHo5iyjcQuVnmigtfv6RsQQ-Cw3CCWBjw65KADGeHhkNzT87fg@mail.gmail.com>
<CAHyXU0zJhh14ZCHKXV5M91N+RvqVVqe8Yy=iEVVxSNSpx=LVCg@mail.gmail.com>
<CAOR=d=13st6GcimEaMD-mMftBkeB7fhhgPWop-CASpFGyHyOaw@mail.gmail.com>
List-Unsubscribe: <mailto:[email protected]?body=unsub%20pgsql-performance>
On Wed, Jul 6, 2016 at 4:48 PM, Scott Marlowe <[email protected]> wrote:
> On Wed, Jul 6, 2016 at 12:13 PM, Merlin Moncure <[email protected]> wrote:
>> Disabling write back cache for write heavy database loads will will
>> destroy it in short order due to write amplication and will generally
>> cause it to underperform hard drives in my experience.
>
> Interesting. We found our best performance with a RAID-5 of 10 800GB
> SSDs (Intel 3500/3700 series) that we got MUCH faster performance with
> all write caching turned off on our LSI MEgaRAID controllers. We went
> from 3 to 4ktps to 15 to 18ktps. And after a year of hard use we still
> show ~90% life left (these machines handle thousands of writes per
> second in real use) It could be that the caching was getting in the
> way of RAID calcs or some other issue. With RAID-1 I have no clue what
> the performance will be with write cache on or off.
Right -- by that I meant disabling the write back cache on the drive
itself, so that all writes are immediately flushed. Disabling write
back on the raid controller should be the right choice; each of these
drives essentially is a 'caching raid controller' for all intents and
purposes. Hardware raid controllers are engineered around performance
and reliability assumptions that are no longer correct in an SSD
world. Personally I would have plugged the drives directly to the
motherboard (assuming it's a got enough lanes) and mounted the raid
against mdadm and compared.
merlin
--
Sent via pgsql-performance mailing list ([email protected])
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance
reply
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: [email protected]
Cc: [email protected], [email protected], [email protected]
Subject: Re: Tuning guidelines for server with 256GB of RAM and SSDs?
In-Reply-To: <CAHyXU0zKE29Uu2_Bq_6O2pUhGLVn8Xs4SLNpSa8gR1z5mOei1A@mail.gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox