CCL: Effect of using SSD for scratch



 Sent to CCL by: Essam Metwally [Essam.Metwally],[certara.com]
 There are many reviews of the topic of SSD vs HDD. A recent comparison
 between the two is available at the following link.
 http://www.tomshardware.com/reviews/ssd-review-benchmark,3139-6.html
 As you can see there, the I/O is definitely the bottleneck.  You can see
 by the charts that you will be well served using a SSD for a scratch file.
  And you are looking at approximately 85% increase in speed by shifting to
 a SSD...
 HOWEVER
 I have not done the comparison with SSD, but I can offer my own
 comparisons between a RAM disk and a high end hard drive. I have achieved
 speed increases between 100x and 1000x just by shifting to a RAM disk. For
 an SSD ,if you carry the 85% increase in speed, you are looking at 15x to
 150x (I would hazard the numbers are far better than that but I'm not in
 the mood to benchmark it...My SSD is in another machine)
 The practicality of such an approach will always be application specific.
 Basically, can you create a large enough drive to be useful for your
 particular application? Do you have enough memory to support the
 simultaneous use of memory for both storage and application?
 A point for consideration, I just picked up 16GB for a MacBook Pro for
 ~$130.  32GB of DDR3 can be had for ~250...  Memory is far cheaper than it
 used to be but SSD's are still cheaper than memory...  Mac is not an ideal
 platform for RAM disks (On mac they are cached by the unified buffer,
 meaning that in some instances you need at least double the RAM of the RAM
 disk... Ie for a fully used 8GB ram disk you need minimally 16GB of memory
 or you trigger paging out to disk... Self-defeating).  I digress...
 In terms of speed for a SATA 6 configuration you are looking at a max of
 600MB/s speed vs RAM at ~6000MB/s (the former is burst speed, the later is
 sequential, not just a burst)
 And this is not restricted to read and write speeds, you measure memory
 latency in nanoseconds vs 10s to 100s of microseconds for a SSD.  This
 translates into finding what you need that much faster... And lets face
 it, with processors as fast as they are, it will make a huge difference.
 This is particularly germane to GPU computing...
 In short, MEMORY IS CHEAP.  When you are talking about a scratch file, and
 you accept the caveat that the contents of such a disk will not survive a
 crash, then this is absolutely the way to go.
 --
 Essam
 ---------------------------
 Dr Essam Metwally
 Senior Fellow
 Tripos International
 A Certara Company
 essam.metwally]_[certara.com
 Tel +314 662 2868
 ---------------------------
 On 4/24/12 14:42, "John McKelvey jmmckel[]gmail.com"
 <owner-chemistry]_[ccl.net> wrote:
 >
 >Sent to CCL by: John McKelvey [jmmckel#gmail.com]
 >CCLers
 >
 >I am looking to buy a machine sort of specific for running
 >Hartree-Fock and DFT codes.  There is always the issue of cpu speed,
 >but for large systems disk-io can be a significant issue, even for the
 >usual scratch file.  Has anyone done any direct or reasonable indirect
 >evaluations around this issue?
 >
 >Many thanks,
 >
 >John
 >
 >
 >
 >--
 >John McKelvey
 >10819 Middleford Pl
 >Ft Wayne, IN 46818
 >260-489-2160
 >jmmckel^^^gmail.com>
 >
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