dzubin@skorpio.Usask.ca (SED's Thomas Dzubin) (01/26/91)
Please excuse the silly questions from a hardware-ignorant system manager: We are currently looking at replacing our (very) aging VAX 11/750 with something else DEC-like to be a VAXcluster boot node and central storage place for other satellite nodes. Now, I could be cheap and get a uVAX 3100 with a couple Gig. of SCSI disk, but if I look at the Systems and Options catalogs that DEC puts out, I find that the MAX I/O throughput for SCSI on the 3100 is 1.5 MB/s. If I wanted to spend a bit more money and go to something Q-bus based in the 3xxx series like a 3400, I could get 4 MB/s on DSSI disks. Now, obviously on the boot node of a cluster, I want to get the most disk throughput, rather than raw CPU speed, right? (In my Sys & Opt. catalog the 3100 is rated @ 3.5 VUPS and the 3400 is 2.4) Obviously, there are other factors such as expandability and bus vs. non-bus computers... ...but... THE QUESTION IS: am I right in saying that the SCSI interface is a major bottleneck making the 3100 a poor choice for a boot node in a small cluster?? My dilemma: I can buy one 3400 or I can buy four 3100s...what to do? Thomas Dzubin SED Systems Inc. #18 Innovation Boulevard, Saskatoon Saskatchewan, Canada dzubin@skorpio.usask.ca "Network Coordinator" (whatever that means) (306) 933-1573
bruce@camb.com (Barton F. Bruce) (01/30/91)
> THE QUESTION IS: am I right in saying that the SCSI interface is a major > bottleneck making the 3100 a poor choice for a boot node in a small cluster?? There are those nice 11 ms 3rd party SCSI drives, or if you want to save a tad, you can buy the slow 15 ms ones. Some brands may be a tad slower but offer 150000 to 200000 hour MTBF WITH a 5 year warantee. Think of all the money you won't pay field service. For what you would have paid DEC, you can buy a pile of them. Do get some processor you can put tons of cheap memory on, and with enough extra CPU power (won't take much more) to run something like Executive Software's IOEXPRESS. IOEXPRESS, given a few cpu cycles and lots of memory, will give you some amazing cache hit percents. The 11 ms disks are very nice, too. Most real world users hit seek time limits, NOT xfer limits. More spindles helps here, too. If you get a Q bus machine with the right 3rd party controller, you can hang CDROMS (for DEC's software distribution + online DOC service), all your disks, and 4 or 8 mm backup tape drives on it. Buying an all DEC solution is great if you can afford it. Mix and match shopping from some OEM that knows what works is often a better deal. Have fun!