you sound like a drive vendor.  I hear exactly this from them too bad
test results prove otherwise.  Good luck.

On Thu, May 01, 2008 at 09:00:04AM -0700, Ralph Becker-Szendy wrote:
> On Wed, Apr 30, 2008 at 01:15:56PM +0100, Dave Ewart wrote:
> > > SSD is currently a myth.  They aren't better faster greater etc.
> > > Maybe the next generation...
> >
> > The advantages of SSD are that it is quieter, uses less power and
> > generates less heat than a conventional drive.  I don't believe anyone
> > promised that the drives would be *faster*, necessarily.  If you want
> > quiet and low power, and have no need of large capacity, then SSD is
> > fine...
>
> This statement is false.  There exist SSD drives that are not a myth,
> and are much much faster than spinning disks.  For example, I have a
> few enterprise-grade SSD drives in my lab that have 73GB capacity, can
> read (both random and sequential) at about 200 MBytes/s sustained, can
> write at about half that speed, and can do about 50 thousand small random
> IOs per second.  The comparison for a typical SATA disk about about
> 90MB/s sustained for read and write, and about 100 small random IOs per
> second; so depending on the workload the SSD is anywhere from slightly
> faster than the spinning disk (all sequential writes) to 500x faster
> than the spinning disk (small random reads).
>
> On Wed, 30 Apr 2008 09:09:30 -0500, Marco Peereboom wrote:
> > Sure but you forget to mention the MTBU.  Currently SSD is lower than
> > SATA drives.
>
> That statement is also false.  The write endurance of modern, high-
> performance SSDs is amazingly high.  I calculated that for an enterprise
> SSD, you can write continuously (the interface is saturated with about
> 100 MBytes/s of writes 24x7x365) for over a year before the flash chips
> wear out.  With a sensible workload (duty cycle is not 100%, and the bulk
> of the IOs are reads and not writes), the endurance will be much larger,
> typically longer than the economic lifespan of the drive (which is about
> 5 years).  Note that the write endurance of an SSD that uses spare capacity
> and wear leveling is quite predictable, and a well-managed drive will
> not fail spontaneously, but give ample warning.
>
> Once the write endurance is out of the way, the MTBU is determined by
> the usual MTBF.  For spinning drives, the drive manufacturers tend to
> quote MTBF numbers of about a million hours; the MTBF actually observed
> in the field under good conditions (enterprise-quality disk arrays
> and rack-mount enclosures in conditioned data centers, not consumer PCs
> with inadequate cooling in residential areas) is about one order of
> magnitude lower (for details, see the proceedings of the two most recent
> FAST conferences, there has been much academic work on disk reliability
> recently).  So we can conservatively assume the MTBF of a spinning SATA
> disk to be about 100K hours; under the assumption of a Poisson failure
> process, this means that about 1 of each 12 disks will fail in a year.
>
> For comparison: The MTBF of flash-based enterprise-grade SSDs is quoted
> by the manufacturer as about 2.5M hours, and industry tests seem to
> confirm that number (unlike spinning disks, where industry tests tend
> to be an order of magnitude worse than vendor claims).  So high-end SSDs
> are probably dozens of times more reliable than spinning disks.
>
> Now, there is the old trifecta: fast, reliable, cheap, pick any two.
> High-end enterprise grade SSDs are not available in a bin at your
> neighborhood computer parts store, nor do they cost $99.  They tend to be
> special order at industrial and enterprise computing vendors, or they are
> available in disk subsystems from high-end vendors (EMC, Hitachi, IBM,
> the usual suspects).  They tend to be about 10x more expensive than
> enterprise-grade (fibre channel or SAS) disks, and per unit capacity
> about 30x more expensive than consumer-grade SATA disks.
>
> I am aware that low-end inexpensive consumer-grade SSDs do exist.  Those
> are neither fast (some of them have ludicrously low write speeds), nor
> very reliable (some of them have low write endurance, comparable to
> little CF cards).  On the other hand, they are priced very attractively.
>
> -- 
> Ralph Becker-Szendy    [EMAIL PROTECTED]            (408)395-1435
> 735 Sunset Ridge Road; Los Gatos, CA 95033

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