zfs discuss - Sep 2008 - Which is better for root ZFS: mlc or slc SSD?

I was under the impression that MLC is the preferred type of SSD, but I
want to prevent myself from having a think-o.


I''m looking to get (2) SSD to use as my boot drive. It looks like I can
get 32GB SSDs composed of either SLC or MLC for roughly equal pricing.
Which would be the better technology?  (I''ll worry about rated access
times/etc of the drives, I''m just wondering about general tech for an
OS
boot drive usage...)



-- 
Erik Trimble
Java System Support
Mailstop:  usca22-123
Phone:  x17195
Santa Clara, CA
Timezone: US/Pacific (GMT-0800)

Erik Trimble wrote:
> I was under the impression that MLC is the preferred type of SSD, but I
> want to prevent myself from having a think-o.
>
>
> I''m looking to get (2) SSD to use as my boot drive. It looks like
I can
> get 32GB SSDs composed of either SLC or MLC for roughly equal pricing.
> Which would be the better technology?  (I''ll worry about rated
access
> times/etc of the drives, I''m just wondering about general tech for
an OS
> boot drive usage...)
>
>
>
>   
SLC is faster and typically more expensive.

On Wed, 24 Sep 2008, Erik Trimble wrote:
> I was under the impression that MLC is the preferred type of SSD, but I
> want to prevent myself from having a think-o.
Depends on what one prefers, I guess.  :-)

SLC is prefered for performance reasons, MLC tends to be cheaper.
I installed an SLC SSD in my Ferrari 3400.  It was SIGNIFICANTLY
faster than the 7200RPM spinning rust it replaced (which was no
slouch itself).
> times/etc of the drives, I''m just wondering about general tech for
an OS
> boot drive usage...)
FWIW, I''d say go with SLC.

-- 
Rich Teer, SCSA, SCNA, SCSECA

CEO,
My Online Home Inventory

URLs: http://www.rite-group.com/rich
      http://www.linkedin.com/in/richteer
      http://www.myonlinehomeinventory.com

On Wed, 24 Sep 2008, Erik Trimble wrote:
> I was under the impression that MLC is the preferred type of SSD, but I
> want to prevent myself from having a think-o.
SLC = Single level
MLC = Multi level

Since the SLC stores only a binary value rather than several possible 
encoded values it becomes more reliable but stores less data per cell.

Bob
=====================================Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

On Wed, Sep 24, 2008 at 1:41 PM, Erik Trimble <Erik.Trimble at sun.com>
wrote:
> I was under the impression that MLC is the preferred type of SSD, but I
> want to prevent myself from having a think-o.
>
>
> I''m looking to get (2) SSD to use as my boot drive. It looks like
I can
> get 32GB SSDs composed of either SLC or MLC for roughly equal pricing.
> Which would be the better technology?  (I''ll worry about rated
access
> times/etc of the drives, I''m just wondering about general tech for
an OS
> boot drive usage...)
>
>
Depends on the MFG.  The new Intel MLC''s have proven to be as fast if
not
faster than the SLC''s, but they also cost just as much.  If they
brought the
price down, I''d say MLC all the way.  All other things being equal
though,
SLC.


--Tim
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On Wed, Sep 24, 2008 at 1:41 PM, Erik Trimble <Erik.Trimble at sun.com>
wrote:
> I was under the impression that MLC is the preferred type of SSD, but I
> want to prevent myself from having a think-o.
MLC - description as to why can be found in....

http://mags.acm.org/communications/200807/

See "Flash Storage Memory" by Adam Leventhal, page 47.

-- 
Mike Gerdts
http://mgerdts.blogspot.com/

Tim wrote:
>
>
> On Wed, Sep 24, 2008 at 1:41 PM, Erik Trimble <Erik.Trimble at sun.com 
> <mailto:Erik.Trimble at sun.com>> wrote:
>
>     I was under the impression that MLC is the preferred type of SSD,
>     but I
>     want to prevent myself from having a think-o.
>
>
>     I''m looking to get (2) SSD to use as my boot drive. It looks
like
>     I can
>     get 32GB SSDs composed of either SLC or MLC for roughly equal pricing.
>     Which would be the better technology?  (I''ll worry about rated
access
>     times/etc of the drives, I''m just wondering about general tech
for
>     an OS
>     boot drive usage...)
>
>
> Depends on the MFG.  The new Intel MLC''s have proven to be as fast
if
> not faster than the SLC''s,
That is not comparing apples to apples.   The new Intel MLCs take the 
slower, lower cost MLC chips,
and put them in parallel channels connected to an internal controller 
chip (think of RAID striping).
That way, they get large aggregate speeds for less total cost.
Other vendors will start to follow this idea.

But if you just take a raw chip in one channel, SLC is faster.

And, in the end, yes, the new intel SSDs are very nice.
> but they also cost just as much.  If they brought the price down,
I''d
> say MLC all the way.  All other things being equal though, SLC.
>
>
> --Tim
> ------------------------------------------------------------------------
>
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
>   
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In general, I think SLC is better, but there are a number of brand-new
MLC devices on the market that are really fast; until a new generation
of SLC devices show up, the MLC drives kind of win by default.

Intel''s supposed to have a SLC drive showing up early next year that
has similar read performance to their new MLC device, but with 2x the
write speed, but that''s at least 3 months out.


Scott

On Wed, Sep 24, 2008 at 12:16 PM, Neal Pollack <Neal.Pollack at sun.com>
wrote:
> Tim wrote:
>
> On Wed, Sep 24, 2008 at 1:41 PM, Erik Trimble <Erik.Trimble at
sun.com> wrote:
>>
>> I was under the impression that MLC is the preferred type of SSD, but I
>> want to prevent myself from having a think-o.
>>
>>
>> I''m looking to get (2) SSD to use as my boot drive. It looks
like I can
>> get 32GB SSDs composed of either SLC or MLC for roughly equal pricing.
>> Which would be the better technology?  (I''ll worry about rated
access
>> times/etc of the drives, I''m just wondering about general tech
for an OS
>> boot drive usage...)
>>
>
> Depends on the MFG.  The new Intel MLC''s have proven to be as fast
if not
> faster than the SLC''s,
>
> That is not comparing apples to apples.   The new Intel MLCs take the
> slower, lower cost MLC chips,
> and put them in parallel channels connected to an internal controller chip
> (think of RAID striping).
> That way, they get large aggregate speeds for less total cost.
> Other vendors will start to follow this idea.
>
> But if you just take a raw chip in one channel, SLC is faster.
>
> And, in the end, yes, the new intel SSDs are very nice.
>
> but they also cost just as much.  If they brought the price down,
I''d say
> MLC all the way.  All other things being equal though, SLC.
>
>
> --Tim
>
> ________________________________
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
>
>
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
>
>

For a root device it doesn''t matter that much. You''re not
going to be
writing to the device at a high data rate so write/erase cycles don''t  
factor much (MLC can sustain about a factor of 10 more). With MLC  
you''ll get 2-4x the capacity for the same price, but again that  
doesn''t matter much for a root device. Performance is typically a bit  
better with SLC -- especially on the write side -- but it''s not such a
huge difference.

The reason you''d use a flash SSD for a boot device is power (with  
maybe a dash of performance), and either SLC or MLC will do just fine.

Adam

On Sep 24, 2008, at 11:41 AM, Erik Trimble wrote:
> I was under the impression that MLC is the preferred type of SSD,  
> but I
> want to prevent myself from having a think-o.
>
>
> I''m looking to get (2) SSD to use as my boot drive. It looks like
I
> can
> get 32GB SSDs composed of either SLC or MLC for roughly equal pricing.
> Which would be the better technology?  (I''ll worry about rated
access
> times/etc of the drives, I''m just wondering about general tech for
> an OS
> boot drive usage...)
>
>
>
> -- 
> Erik Trimble
> Java System Support
> Mailstop:  usca22-123
> Phone:  x17195
> Santa Clara, CA
> Timezone: US/Pacific (GMT-0800)
>
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss

--
Adam Leventhal, Fishworks                        http://blogs.sun.com/ahl

Adam Leventhal wrote:
> For a root device it doesn''t matter that much. You''re not
going to be
> writing to the device at a high data rate so write/erase cycles
don''t
> factor much (MLC can sustain about a factor of 10 more). With MLC  
> you''ll get 2-4x the capacity for the same price, but again that  
> doesn''t matter much for a root device. Performance is typically a
bit
> better with SLC -- especially on the write side -- but it''s not
such a
> huge difference.
> 
> The reason you''d use a flash SSD for a boot device is power (with
> maybe a dash of performance), and either SLC or MLC will do just fine.
Or available physical space in the case.  For example a home server or 
small consumer NAS appliance where you want to maximize the space 
available for the "user data" ZFS pool and keep the OS in a completely
separate pool but don''t have the space for even a 2.5" drive.

This is exactly the situation have have and I''m planning on migrating 
the OS to a consumer SSD (A San Disk Extreme III) via an IDE/CF adaptor, 
thus keeping OS and data pools separate.

-- 
Darren J Moffat