On Fri, May 23, 2003 at 06:05:15PM +0200, Roberto Sanchez wrote: > Just out of curiousity. Is it worth it to get a SCSI hard drive now? I mean, > is there enough selection of drives and mobos with onboard SCSI to make them > available at a good enough price? (I ask because I am looking into buidling a > new machine in the near future). I would say so - definitely... HDs seem to come in sizes of m * 2^n; for IDE HDs m is often 10 and for SCSI HDs 9 seems to be common. I've found that at least for small values of n, SCSI HDs seem to be available for 50-75% more than an IDE HD with the same n. (You will also find similar spec drives, or even the same drive, being sold for 300-500% more. www.dealtime.co.uk is a useful way to avoid this sort of nonsense.) Make sure you check out the data sheet before you buy a drive so you know what you're getting. SCSI controllers... not sure what you can get built into the MB. PCI cards seem to start from forty pounds or so in the UK (excluding those that only do 8-bit SCSI) up to a couple of hundred depending on capabilities; again check www.dealtime.co.uk to avoid getting seriously ripped off. I'd recommend hunting for second hand cards. Before you buy any card, new or secondhand, google for its exact type number and read the data sheet. Capabilities vary widely, and there are still plenty of cards being produced new that only support relatively old versions of SCSI. SCSI drives tend to have faster spindle speeds than IDE, so the raw transfer rate between platter and head, which tends to be the limiting factor on sufficiently large file operations, is faster than IDE. For smaller operations, the SCSI bus protocol is much more economical with processor time than IDE, and the drives seem to be more intelligent at caching. The result is that responsiveness is improved even if you compare a slower SCSI bus with a faster IDE one. SCSI drives are able to transparently remap the data from a block which is becoming hard to read onto a clean block, which is good for reliability. The number of such mappings can be checked by reading the grown defects table with scsiinfo to provide an easy means of seeing whether the drive is on its last legs. Because a SCSI bus can support up to 16 devices (including the controller) it is easy to string together a large number of secondhand drives to get cheap capacious storage. I like to buy them in pairs and set them up as ext3 with external journals, each drive of the pair holding the external journal of the other drive. This is faster than the conventional ext3 with the journal on the same device. If you want to do hardware RAID it is said to work much better on SCSI than IDE, especially as regards hot-swapping and/or the "unplug a drive and see if it still works" test. The disadvantages of SCSI are that it is undeniably more expensive, and that while it is possible to plug any SCSI drive into any SCSI card and it'll work, to get the best performance out of the combination it is necessary to do some research (unless you are in the fortunate position of being able to spend unlimited money on top-of-the range kit). I find it is useful to ignore all the Fast Wide SCSI Ultra Enigma jmre ghry because those terms are often used very "loosely" for marketing reasons: it's better to dig into the data sheet for the raw figures on bus width and transfer rate, and whether this is achieved with active or passive termination, SE or LVD etc. It is still not unknown to find marketroids' dirty fingerprints in the raw data, so be prepared to be confused! -- Pigeon Be kind to pigeons Get my GPG key here: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x21C61F7F
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