> > > Thus in the case of SCSI where you cannot (by definition) overcome the > > > number of 6 devices x chain/controller, > > > > WHAT SCSI are you talking about? Try 16. not 6. > > > > How many addresses have you per controller ? > from 0 to 6 = 7 but 1 is the controller itself. > SCSI is not IBM SSA . SCSI = 6 devices x controller/chain ; SSA > 16 devices x > controller/loop
No one uses narrow SCSI for RAID, and it doesn't have to be SSA. SCSI uses four bits for SCSI ID, which makes SIXTEEN devices. > > That's not true. There is no "double write", both the data/parity is > > written at the same time. Parity can easily be calculated on the fly. > > > > YEP ! and who does write it on the disk in a different area/zone/disk ? A correct implementation of RAID 5 will write all at the same time. RAID 5 is NOT slowed down because it has to do multiple writes, it's because, sometimes, depending on stripe size, it has to read, calculate parity, then write. RAID 5 is slowed down for reads, since the parity is distributed across drives. > > Run some benchmarks on your system and see for your self. > Also, make sure > > the benchmarks AREN'T running out of disk cache...that hardly tests the > disk > > speed. You'll be lucky to get even near 80, if even 60. > > My data are the output of a benchmark and not the theoretical max speed. What benchmark are you using? I do not believe you are getting 134M bytes/sec, it is physically impossible. > Yes you can add because SCSI can parallelize the requests while > IDE cannot. IDE CAN parallelize, and as I said, you can't just add transfer rates, it doesn't work that way. > > The standard PCI bus is 33 MHz (or 66MHz), NOT 133MHz. Perhaps you mean > > 132M BYTES/sec? Even at that, you can't get near %80 of that, if you're > > lucky. 132M bytes/sec is the burst rate. There is substantial overhead > on > > the PCI bus that lowers that substantially. > > > > YEP ! I can achieve the saturation of bus before achieving the > saturation of > the controller (Adaptec 29160 is a 64 bit adapter). Now you're talking silly. You said you had four disks. The MAX media transfer rate from those disks is around 35M bytes/sec. Even if they were able (which they are NOT) to sustain that over the SCSI/PCI bus at full speed, that's 140M bytes/sec. 64 bit PCI is 264M bytes/sec for 33MHz PCI, and 528M bytes/sec for 66MHz PCI...so there is NO way you are saturating the PCI bus especially with a 64 bit controller. You previously said you were on a 32 bit PCI bus.