Sorry if this is long but it is important to users of classic machines. <I gently disagree with this assertion that ST251 series is good than <ST225 series. I got too many dead ST251 series compared to ST225's <due to weaker structral design, pushed design by driving steppers too <hard byond 40ms average and not as rugged as ST225's. Can't say I disagree. You however confused my assertion of better performace in terms of access times, with reliability. Its faster and more storage for less power and heat than two st225s. I never said it was more reliable. My expereince is that the st251 is less tolerrent of heat but if cooled it seems to do as well as most st225s (n=10k+). An experience with a customer in Austrailia using both 225s and 251s proved it. FYI neither like heat! <goal set by designers. If one wants faster seeking time, go voice <coil! I am dreaming wishing that ST251 drive was fitted with voice <coil instead of stepper and better motor design...sigh. true, but there are voice coil dries out there that do not hold up well too. It's a design trade made by some companies thinking the mechanics will never outlive the electronics. Much of it is process quality and handling. Most bad drives I've seen were from warm enviornments or dropped in their life. <reliably. Whole problem was that design of this ST251 spindle motor <is ill-designed to begin with in my opinion: Trying to fit all the <coils and one bearing INSIDE that spindle results in weak axle that <gets bent easily due to this design and the bearings failure rate on <this one is high too. It has a problem with gyroscopc precession, this makes it very susceptable to small shocks when running. The bearing does not like sideloads either. I agree it could have been better thought out. generally going to the smaller 3.5" was actaully an improvement in reliability for disks as it took less power to spin it and also move the heads. With less mass in the media the motors, bearings and all could be more rigid for it's size. The lower heat made bearing life better and also helped dimesional stability. < Recently I pulled this ST225 out of dumpter and fixed up the XT with < this hd and LLF'ed it. Gave whole thing to poor guy to use vax at < college. Still works. Most 225s were not fails, just retired due to small space available. FYI you get better results if the disk is LLF'd in situ and well warmed up. I must have 6 st225s of them all good and solid. I use them but, when I need speed I try to use others (quantum q540 30mb is nice!). <I tore down all kinds of drives from old and 3 years old types for <post-failure analysis which gave pretty good info for me. Same here, mostly limited to: St506, st412, st225, st251, micropolus1325 and quantum Q540, Q2190s and a few other dec disks. I have an st238 that refuses to die! <Snip! Tales of positive things about cooling... <Actually, all drives old and new benefits from cooling and boards <likes the flowing cooling air. Very true, vacuuming the vents from time to time also is a good thing. The big advantage of the newer drives is they consume less power therfore produce less damaging heat enhancing reliability. <We have no choice as many do not have AC so they ran in warm air <but if you are careful, enough fans to make hurriance out of it and <put a fan or two on monitor as well. My 17" needs two otherwise the <HOT transistor will pop again. ARRGgghhh. Tell me! I run microvaxen, Q-bus PDP-11s and s100 systems and 20 years of experince (and reliability studies) has taught me 90F is a hard ceiling and to shutdown with fans running if it gets hotter. I know this from my days at DEC in the mill when my office system (11/23) was fried by an AC failure, the area hit 98f and the 11 went down for the count. I've been pulling the plug regularly this year as we've had a lot of warm here in MA. ;-) Even without AC, every effort to remove heat is good! Even if you can't lower the ambient, keeping the guts closer to it will help greatly. My s100 crate has two 5" 120cfm fans pushing air up through the cage and it runs stone cold. The original layout had an 80cfm fan in the PS section pulling the air around and the boards ran HOT. It makes a racket but compared the the 8" drive and considering it's 20 years old... it still runs. Even my ba123 microvax, I replaced the fans to blow up as someone put them in backwards for less noise. You fight convection and lose cooling efficiencty. Since I have few spares I prefer to keep it going and tolerate a slight increase in noise. This is something to watch for on older systems where things may have been replaced but with the wrong (underrated) items. One last item. MAKE BACKUPS OF EVERYTHING. make duplicate backups and test the backups for integrity. Disks fail, and the cheapest insurance is a boot and backup package that works when you replace/repair the offending drive. Allison