On Jan 24, 8:58 pm, Kris Tilford <ktilfo...@cox.net> wrote:
> I learned this THE HARD WAY, I actually BOUGHT FW800 enclosures > expecting them to be TWICE AS FAST as my old FW400 enclosures, but > when I TESTED THEM, they were the SAME SPEED, not because they're not > CAPABLE of twice as fast, but because you'd need a RAID of multiple > HDs to saturate the connection. This whole 1.5 Gbps or 3.0 Gbps thing > for individual HDs is 100% hype. No single HD can sustain anything > near that rate. Mechanical LATENCY is the reason. It doesn't matter > how fast the electronics can move bits when the mechanical parts can't > move equally as fast. <grinning> I learned this exact same lesson in the mid-90s. On Nubus machines... I finally had a PPC NuBus machine (8100 clone) and a I got the holy grail of interface cards, the FWB Jackhammer Fast & Wide SCSI card. I had an assortment of ST32550 drives, some N (narrow, 50 pin) and some W (wide, 68 pin). The 32550 was the latest, fastest Barracuda from Seagate and was amongst the very first 7200 RPM drive available. A single ST32550W on the JackHammer really didn't provide any better performance than a single ST32550N on the built-in busses, even though the specifications say 20MB/s vs. 10MB/s. What! But it should be so much faster! Then I built a RAID of four ST32550W on the JackHammer. I got maybe 8MB/s actual performance out of it. It was actually faster to have a RAID of two ST32550W drives than it was to have four of them. I ultimately found that the fastest RAID was two ST32550Ws on the JackHammer, one ST32550N on the built-in Fast SCSI bus, and one ST32550N on the built-in non-Fast bus. That got me about 12MB/s or twice what a single drive could deliver. Anyway, point is, sure the electronics could do 20 MB/s (maybe) but the drives back then could only output maybe 6 MB/s each and as one tried to gang those up in a RAID, inefficiencies in the infrastructure ate up a lot of the potential performance. Of course, drives today are almost ten times faster (more than?) but the principles haven't changed a bit. A 133 MB/s interface doesn't matter one wit, if the drive can only deliver 70MB/s of data. Jeff Walther -- You received this message because you are a member of G-Group, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to g3-5-list@googlegroups.com For more options, visit this group at http://groups.google.com/group/g3-5-list
