From owner-chemistry@ccl.net Wed Apr 25 00:32:01 2012 From: "Essam Metwally Essam.Metwally]~[certara.com" To: CCL Subject: CCL: Effect of using SSD for scratch Message-Id: <-46784-120424231525-30364-F3Ylk8zQagdUMdO6XE5u3g]![server.ccl.net> X-Original-From: Essam Metwally Content-Language: en-US Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" Date: Tue, 24 Apr 2012 22:15:10 -0500 MIME-Version: 1.0 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" 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> > _________________________________________________________________ NOTICE: The information contained in this electronic mail message is intended only for the personal and confidential use of the designated recipient(s) named above. This message may be an attorney-client communication, may be protected by the work product doctrine, and may be subject to a protective order. As such, this message is privileged and confidential. If the reader of this message is not the intended recipient or an agent responsible for delivering it to the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify us immediately by telephone and e-mail and destroy any and all copies of this message in your possession (whether hard copies or electronically stored copies). Thank you.