On 5/10/06, Alan Dayley wrote: > > Trent Shipley said: > > There has been a discussion about drive interface standards on the > Postgresql > > general list. I don't understand it. > > Your questions are very broad. Maybe some context of the discussion would > help to narrow the focus a bit. Let me provide some specific bullet > points. > > > What is the difference between IDE, SSCI, ATA, and SATA? > > - IDE (Integrated Drive Electronics) is the early marketing term for ATA > (Advanced Technology Attachment). They are really the same. [1] > > - You didn't mention ATAPI (Advanced Technology Attachment Packet > Interface) with started as an extension to ATA for support of removable > media drives like CD-ROM and Iomega ZIP drives. Probably because ATAPI > hard disks don't exist. In any case, ATAPI is part of the ATA protocol > specification now. > > - SATA (Serial ATA) is an update to ATA to transfer the same command set > over serial channels instead of a parallel bus. [2] > > - Because of SATA, the term PATA (Parallel ATA) is now being applied to > the original ATA devices. ie. IDE == ATA == PATA. > > - SCSI (Small Computer System Interface) has been around a long time > compared to ATA with it's roots going back to 1979. It handles devices of > many types (scanners, tape drives, media changers, etc.) besides hard disk > drives. > > - You did not mention a new tech called SAS (Serial Attached SCSI) which > is similar in nature to the ATA-->SATA evolution. That is, transmitting > the same SCSI commands in serial packets. [4] > > > What are the > > implications for: > > drives on notebooks and PCs > > This maybe best answered by looking at the goals of each protocol. I'll > reduced them to ATA vs. SCSI since the rest are flavors of one or the > other. > > The original goal of ATA was to provide an inexpensive "consumer grade" > hard drive interface. SCSI, from the beginning, was intended for reliable > "systems or industrial grade" data operations, including higher > performance. As a result of these somewhat opposing goals ATA > technologies are common in the consumer computer world and ATA devices > tend to be less expensive per MB. SCSI devices are very common in > industrial applications, servers and main frames, for example and are more > expensive per MB. SCSI fans look down on ATA devices as cheap and prone > to failure sooner rather than later. ATA fans look down on SCSI devices > as overly expensive and over engineered. > > Truth is that, whether by side effect of improving technologies or by > design, ATA is evolving to be just as good and fast as SCSI. Believe it > or not but there are still far more SCSI storage systems in use today than > ATA but ATA use is multiplying very fast and is taking over uses where > SCSI was traditionally deployed. It used to be that finding ATA drives > with high duty cycles and MTBF was difficult but that is changing. > > The bottom line is that you'd be hard pressed to find a notebook with a > SCSI hard drive in it. Similarly you'd be hard pressed to find a > mainframe or heavy industrial computer with an ATA drive. But the two are > converging both in terms of price and capabilities. > > > low TB drive arrays > > SAN? > > Drive arrays and SAN and NAS, etc. are technologies either combining or > sharing (or both) storage to a host or across a network. This is a layer > "above" the actual hard disk interface layer represented as SCSI or ATA or > one of it's flavors. In other words, you could have a SAN server that > uses ATA drives and another that uses SCSI and both would interact with > the network layer exactly the same. Clients using the storage would not > know what hard drive protocol is used. > > So, how the hard drive protocol effects the network storage technology > manifests in only in how reliable, fast, etc. the interface operates. One > who believes SCSI is best in a SAN service probably believes it is best in > every other situation for the same reasons. Some dismiss ATA as a viable > server interface because of it's history as consumer grade. I can accept > such a thought as a rule of thumb but not as universally true. > > A server is general powered and operating for 24/7 so the most important > specification is the drive's duty cycle. How many hours per 24 is the > drive designed to be operating? The duty cycle of most ATA drives is 10 > hours or less per 24. (There are more and more that have a 24 hour cycle > but they'll cost you.) Using such a drive in a server is not "wrong" if > you have a good data backup process that you actually follow and you are > willing to save money on each drive but probably buy them more often. > > Corrections and discussions are invited. > > Alan > > [1] http://en.wikipedia.org/wiki/Integrated_Drive_Electronics > [2] http://en.wikipedia.org/wiki/Serial_ATA > [3] http://en.wikipedia.org/wiki/SCSI > [4] http://en.wikipedia.org/wiki/Serial_Attached_SCSI > > PS Wikipedia is wonderful! > > > --------------------------------------------------- > PLUG-discuss mailing list - PLUG-discuss@lists.plug.phoenix.az.us > To subscribe, unsubscribe, or to change you mail settings: > http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss > If the Main PLUG discussion list has an FAQ archive, or any kind of "BEST of" the all-stars (all-time helpful posts) log, then I would nominate this [answer from Alan Dayley], for such an honor. -- Mike Schwartz Glendale AZ schwartz@acm.org Mike.L.Schwartz@gmail.com