Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!van-bc! From: lphillips@lpami.wimsey.bc.ca (Larry Phillips) Newsgroups: comp.sys.amiga.hardware Subject: Re: Hard disk transfer rates Message-ID: <1920@lpami.wimsey.bc.ca> Date: 1 Sep 90 21:03:58 GMT Lines: 88 Return-Path: To: van-bc!rnews In <1990Sep1.231510.10650@agate.berkeley.edu>, c60c-1gd@e260-1c.berkeley.edu (Joon Song) writes: >I'm sorry if this has been discussed before. I've read several articles >claiming that hard disk transfer rates through a SCSI port is as high as >3.5 meg/sec. Is this the actual throughput of the hard disk system? >Does this involve data being cached? 3.5 meg/sec is considerably faster >than what I had thought possible for hard disk r/w. There are hard drives, and there are hard drives. Some are faster than others. The fastest hard drives are fairly expensive, though not exceedingly so. >Suppose a hard disk had 34 sectors/track. A hard disk spins 60 rev/sec. >So the fastest disk transfer rate should be: > 34 sectors/track * 512 bytes/sector * 60 rev/sec = approx. 1 meg/sec. Suppose it had cylinder caching. Suppose it had even more sectors per track. Suppose it had a parallel head scheme. Suppose it is an SMD drive run through a SCSI<->SMD adapter. >Can someone explain how 3.5 meg/sec transfer rate can be possible? Many things are possible, once the drive and controller are integrated, and the manufacturer no longer has to have a controller<->drive interface that is compatible with any published standards. The fastest SCSI hard drives available today can run pretty fast. Here are some excerpts from a posting on another newsgroup: -------------------------------------------------------------------------- Synchronous SCSI is a data transfer method that, during the data phase only, allows burst data transfers at a higher rate over a longer distance than asynchronous transfer allows. Depending on the particular machines, the data rates theoretically reach 5 Mbytes. Typical implementations allow 2.5 to 4.5 Mbytes. The host adapter and the peripheral device must both agree, through a special negotiation procedure, what speed they will use. Note that most SCSI disk drives are ultimately limited in their data rate by the rate at which data can be read from the disk, typically 1.2 to 1.8 Mbytes. SCSI disk drives are just beginning to get their seek times down near SMD seek times (14 to 20 milliseconds). The result is that, for the near term, the net performance of a typical SCSI drive will be somewhat less than the performance of an SMD disk drive. As the disk data rate and seek times improve over the next five years, the SCSI drives will gradually move into the performance range presently occupied by the SMD drives. Many of the SCSI disks also have special caching and buffering features that not only speed up the data transfer, but provide faster access to the data. ----------------------------------------------------------------------- The Imprimis Wren-7 is a 1.2GB drive with a sub-20ms average access time and up to 4MB/sec synchronous SCSI transfer rate. Hewlett-Packard also makes a 1.2GB SCSI drive with 16ms average access time, 4MByte/sec transfer rate synchronous, 1.5MByte/sec asynchronous. The Imprimis drive (without power supply or cabinet) is available from Arrow Electronics for ~$4000. The HP drive is available from Hybrid Systems (+1 617 357 1838) for $4150. It comes with a 5-year warrantee from HP. Besides the benefit of a 40% price reduction, these are 5-1/4'' drives, taking trivial space and power and not requiring rack mounting. (Hybrid can also sell you the Imprimis drive, and packaging and cables and such.) My HP drive is "in the mail" and I can let you know how it works in a few weeks. I've had nothing but pleasure from my two Imprimis Wren-5's so I expect that a Wren-7 would do fine too. It was the 5-year warrantee from HP that swayed me in their direction. I don't know of any SCSI drives that have hit the 6MB/sec transfer rate of the $11500 IPI drives, but for that money you could buy TWO 1.2gig SCSI disks and TWO host adapters, for a similar aggregate data rate but twice the access arms, twice the capacity, and the ability to transfer data on one drive while the other is seeking. --------------------------------------------------------------------------- -larry -- It is not possible to both understand and appreciate Intel CPUs. -D.Wolfskill +-----------------------------------------------------------------------+ | // Larry Phillips | | \X/ lphillips@lpami.wimsey.bc.ca -or- uunet!van-bc!lpami!lphillips | | COMPUSERVE: 76703,4322 -or- 76703.4322@compuserve.com | +-----------------------------------------------------------------------+