[email protected] (Timothy Sipples) writes: > Percentage/ratio cost differences are not *exactly* what drive cost-based > decisions. To illustrate why, consider these two hypothetical scenarios: > > 1. A 1 TB hard disk costs $100 and a 1 TB SSD costs $1000. > 2. A 1 TB hard disk costs $1 and a 1 TB SSD costs $10. > > In both cases the SSD is 10 times more expensive -- 1000%. But in Case #2 > *both* are more affordable -- both experience 99% price drops -- and both > more easily fit within more budgets. SSD only has to get "affordable > enough" to take over more use cases from hard disks. Said another way, > absolute prices matter. Said yet another way, the zero lower bound matters. > > A lot of people overlook this reality, but it's a frequent phenomenon in > many markets.
the PC market with $400-$500 computers would be more price sensitve in that range ... however there is the issue is how much do the slower or faster disks affect total system throughput bottleneck. Said another way, it is the relative system costs that matter (and how it contributes to total system throughput). I've periodically mentioned starting to observe in the 70s that disks were increasingly becoming the bottleneck in overall system throughput. In the early 80s, I wrote a paper claiming that disk's relative system throughput had declined by an order of magnitude over the previous 15yrs ... systems got 40-50 times faster while disks got only 4-5 times faster. Disk division executives took exception and assigned the division performance group to refute the statement ... after a couple weeks they came back and effectively said that I had slightly understated the problem. The analysis is then respun and turns into a SHARE presentation on how to optimize disk for system throughput. About the same time there were issues about how datacenter executives view disk costs based on pure price/megabyte ... they would insist on filling the (new) 3380 disk drives completely full of data ... or otherwise they were "wasting" money having half empty 3380s. The issue was having extra data filling 3380s interferred with disk arm optimization and accesses for high used data ... degrading overall system throughput (to save a couple dollars per megabyte on disk they were willing to sacrifice degraded system throughput of system that overall ran to tens of millions). There was a semi-facetious proposal floating at SHARE that IBM announce a special high-performance 3380 that was much "smaller", "faster" and "more expensive" than standard 3380 disk (with much higher cost/megabyte) that would boost overall system throughput. In reality it was just a 3880 microcode load that restricted arm access to only 1/3rd the cylinders. This was something that a datacenter executive could do all on their own with standard 3380 at less cost ... but many appeared to be unable to make that leap. There is recent thread in comp.arch newsgroup about memory being the new disk and disk being the new tape. If memory & disk access latencies are measured in number of processor cycles ... the current latency for memory access measured in number of modern day processor cycles then is on the same order of 60s disk access latency when measured in 60s processor cycles. SSD then might be considered closer to fast tape. But for systems that are fully utilized and disk throughput is bottleneck factor for overall system throughput ... then spending thousands of dollars on more expensive disks might gain several percent increased total system throughput (for overall datacenter that runs several tens of millions, especially factoring in total datacenter costs, hardware, cooling, building, people, etc). Having large controller caches and using memory for keeping large amount of high use information ... complicates the analysis. some recent posts mention SHARE B874 (disk performance group respun analysis) http://www.garlic.com/~lynn/2011.html#35 CKD DASD http://www.garlic.com/~lynn/2011.html#61 Speed of Old Hard Disks http://www.garlic.com/~lynn/2011e.html#1 Multiple Virtual Memory http://www.garlic.com/~lynn/2011g.html#59 Is the magic and romance killed by Windows (and Linux)? http://www.garlic.com/~lynn/2011p.html#5 Why are organizations sticking with mainframes? http://www.garlic.com/~lynn/2011p.html#32 Has anyone successfully migrated off mainframes? http://www.garlic.com/~lynn/2012b.html#73 Tape vs DASD - Speed/time/CPU utilization http://www.garlic.com/~lynn/2012e.html#39 A bit of IBM System 360 nostalgia http://www.garlic.com/~lynn/2012o.html#62 ISO documentation of IBM 3375, 3380 and 3390 track format http://www.garlic.com/~lynn/2013m.html#72 'Free Unix!': The world-changing proclamation made 30 years agotoday http://www.garlic.com/~lynn/2014b.html#49 Mac at 30: A love/hate relationship from the support front http://www.garlic.com/~lynn/2014l.html#90 What's the difference between doing performance in a mainframe environment versus doing in others -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
