Revisiting the Five-Minute Rule 153
In 1987, a study published by Jim Gray and Gianfranco Putzolu evaluated the trade-offs between holding data in memory and storing it on a disk. Known widely as the "five-minute rule," their research was updated and expanded 10 years later. Now, as jamie points out, Communications of the ACM is running an article by Goetz Graefe with another decennial update, evaluating the rule using hardware and software typical of 2007, with an eye toward how flash memory will affect the situation. An excerpt from Graefe's conclusion:
"The 20-year-old five-minute rule for RAM and disks still holds, but for ever-larger disk pages. Moreover, it should be augmented by two new five-minute rules: one for small pages moving between RAM and flash memory and one for large pages moving between flash memory and traditional disks. For small pages moving between RAM and disk, Gray and Putzolu were amazingly accurate in predicting a five-hour break-even point two decades into the future. Research into flash memory and its place in system architectures is urgent and important. Within a few years, flash memory will be used to fill the gap between traditional RAM and traditional disk drives in many operating systems, file systems, and database systems."
for those wondering: (Score:5, Informative)
"The 5-minute random rule: cache randomly accessed disk pages that are re-used every 5 minutes."
Re:OS patches? (Score:3, Informative)
I propose a physical switch to toggle between read/write and read only.
And have social engineers disguise malware as OS updates or dancing bunnies [msdn.com], prompting the home user who doesn't understand risks to flip the switch to see the dancing bunnies.
Re:Flash memory? (Score:4, Informative)
I couldn't quite figure out if the article willfully ignored the advent of SSDs or was written before they were available... As for the post by Argent, I wasn't sure if that was addressed to me or not - if so, I have no idea what you're talking about. Your post has absolutely nothing to do to with my original response.
Argent's post refers to "flash memory". You said the article ignored SSD's, however it did not. "Flash memory" is the technology that SSD's are composed of. Did you not know this? "Flash memory" is all over the article.
Flash SSD's will not replace SATA drives anytime within the next 4-6 years. In technology time, that's such long period of time, it would be quite difficult to make a credible projection for the consumer market space. For servers, where the segment is dominated by 10K/15K drives, you can expect flip over within 18 months.
C//
Re:Flash memory? (Score:2, Informative)
Flash is an SSD, but not every SSD is flash...
Re:What article? (Score:5, Informative)
Hybrid systems are rare, and it doesn't look like they will become more common.
You're probably right when we talk about desktop PCs and laptops. I'm sure the latter will be SSD only in 5-10 years time, and desktops are also losing terrain quickly against laptops.
But when we look at datacenter grade enterprise storage, hybrid systems are currently picking up fast. The advantage is that because of the fast 'flash memory cache' you can use SATA disks instead of the FC/SCSI drives, where the former are both much bigger and much cheaper. Instead of 300 146GB 15K FC disks, you only need 30 1.5 TB 7200 RPM SATA disks. For the same capacity this results in much lower power bills, less DC floor-space costs and much better performance.
If you say "There are some hybrid SAN's, but they're damn expensive.", have a look at what [shameless plug-on] Sun is doing [sun.com], and yes, I work for Sun [plug-off]. But other storage vendors (NetApps, EMC, IBM, etc.) are starting to do similar things.
So the whole "storage-stack" gets more and more hybrid and integrated. It consists of the full gamut of DRAM, flash memory, hard drives and finally tape. Each of these have their own strength and are used best in combination.