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Re: Intel's X25-M SSD

From: "Scott Carey" <scott(at)richrelevance(dot)com>
To: "Greg Smith" <gsmith(at)gregsmith(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Intel's X25-M SSD
Date: 2008-09-09 00:19:49
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Lists: pgsql-performance
I have been paying close attention to the recent SSD performance/price
changes with a keen eye to server performance on various workloads and

The real barrier is in the controller design, and IP surrounding that.  All
flash products with any amount of wear-leveling map logical addresses to
physical flash addresses dynamically.  An intelligent controller, with
enough processing power and RAM (Intel's drive has 16MB of DDR SDRAM) and an
intelligent design can translate ALL random writes into a sequential
stream.  With enough overprovisioning, the erasing and cleaning that goes on
in the background will have very minimal impact.  One thing many people will
claim about a SSD is that the erasing and block management will get slower
as the drive becomes more full.  This is incorrect -- from the point of view
of any block device it is always 100% full, it is not privy to the file
system notion of 'free space'.  Addresses are simply overwritten, which
makes blocks that previously mapped to those addresses available for
writing.  By definition, every write is an overwrite.

This paper, is very enlightening:

Given Intel's particular strenghts and engineering resources, its not a
surprise that they are among the first to make a design like this (FusioIO
seems to have solved the random write performance issue as well ?).  But as
the review you provided links to demonstrates, it is this IP that will
provide the performance gains necessary for flash performance to be hands
down better than all drives, for all workloads, all the time. It is the same
IP that will provide the most longevity and reliability.

Also of note for others reading this thread, the review was for Intel's
"mainstream" device, not the "enterprise" one.  The enterprise one claims
3300 random 4k writes/sec and over twice the write throughput.  I'm sure it
will also cost twice as much for less capacity.

Of particular interest in the short term may be using cheaper, read-biased
flash drives for ZFS L2ARC caches for a database -- it may be like running
with a couple hundred extra gigs of RAM, but you can still use slow, big
drives for mass storage.  The price is prohibitive for putting your whole db
on flash if it is not a small one, but this is not true if you're just
talking about cache devices or xlogs or temp space.

On Mon, Sep 8, 2008 at 4:12 PM, Greg Smith <gsmith(at)gregsmith(dot)com> wrote:

> If like me you've been reading all the flash SSD drive reviews that come
> out, you might have also noticed that the performance on write-heavy
> workloads hasn't been too far ahead of traditional drives.  It's typically
> been hit or miss as to whether the SDD would really be all that much faster
> on a real OLTP-ish database workload, compared to a good 10k or 15k drive
> (WD's Velociraptor is the usual comparison drive).
> That's over as of today:
> You can see what I was talking about above in their Database graph: under
> heavy load, the Velociraptor pulls ahead of even a good performing flash
> product (Samsung's FlashSSD), and the latency curve on the next page shows
> something similar.  But the Intel drive is obviously a whole different class
> of SSD implementation altogether.  It's not clear yet if that's because of
> their NCQ support, or maybe the firmware just buffers writes better (they
> should have tested with NCQ disabled to nail that down).
> With entry-level 64GB Flash drives now available for just under $200 (
> , price is
> so low because they're closing that model out for a better V2 product) this
> space is really getting interesting.
> --
> * Greg Smith gsmith(at)gregsmith(dot)com Baltimore, MD
> --
> Sent via pgsql-performance mailing list (pgsql-performance(at)postgresql(dot)org)
> To make changes to your subscription:

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Subject: best use of another drive
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Subject: Re: Intel's X25-M SSD

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