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Re: Intel's X25-M SSD

From: "Scott Carey" <scott(at)richrelevance(dot)com>
To: "Bruce Momjian" <bruce(at)momjian(dot)us>
Cc: "Greg Smith" <gsmith(at)gregsmith(dot)com>, "Merlin Moncure" <mmoncure(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Intel's X25-M SSD
Date: 2008-09-24 04:25:26
Message-ID: a1ec7d000809232125w52b1122ema21a9958814224b2@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
A fantastic review on this issue appeared in July:
http://www.alternativerecursion.info/?p=106
And then the same tests on a RiData SSD show that they are the same drive
with the same characteristics:
http://www.alternativerecursion.info/?p=276

Most blamed it on MLC being "slow" to write compared to SLC.  Technically,
it is slower, but not by a whole lot -- we're talking a low level difference
of tens of microseconds.  A 250ms latency indicates an issue with the
controller chip.  SLC and MLC share similar overall performance
characteristics at the millisecond level.  The truth is that MLC designs
were low cost designs without a lot of investment in the controller chip.
The SLC designs were higher cost designs that focused early on on making
smarter and more expensive controllers.  SLC will always have an advantage,
but it isn't going to be by several orders of magnitude like it was before
Intel's drive appeared.  Its going to be by factors of ~2 to 4 on random
writes in the long run.  However, for all flash based SSD devices, there are
design tradeoffs to make.  Maximizing writes sacrifices reads, maximizing
random access performance reduces streaming performance and capacity.  We'll
have a variety of devices with varying characteristics optimal for different
tasks.

On Tue, Sep 23, 2008 at 8:24 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> Greg Smith wrote:
> > On Mon, 8 Sep 2008, Merlin Moncure wrote:
> >
> > > What's interesting about the X25 is that they managed to pull the
> > > numbers they got out of a MLC flash product.  They managed this with a
> > > DRAM buffer and the custom controller.
> >
> > I finally found a good analysis of what's wrong with most of the cheap
> MLC
> > drives:
> >
> > http://www.anandtech.com/cpuchipsets/intel/showdoc.aspx?i=3403&p=7
> >
> > 240ms random write latency...wow, no wonder I keep hearing so many
> reports
> > of cheap SSD just performing miserably.  JMicron is one of those
> companies
> > I really avoid, never seen a design from them that wasn't cheap junk.
> > Shame their awful part is in so many of the MLC flash products.
>
> I am surprised it too so long to identify the problem.
>
> --
>  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
>  EnterpriseDB                             http://enterprisedb.com
>
>  + If your life is a hard drive, Christ can be your backup. +
>
> --
> Sent via pgsql-performance mailing list (pgsql-performance(at)postgresql(dot)org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-performance
>

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