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
