[Tfug] Server purchase (!)

[Claude Rubinson]

Ahh... This is the type of information that I needed.  Helps me to
make a more informed cost/benefit analysis.  Thanks a lot!

C.

On Thu, Oct 12, 2006 at 09:17:44AM -0700, Bexley Hall wrote:
> 
> --- Brian Masur <bcmasur at hotmail.com> wrote:
> 
> > All electronics (especially ones with moving parts,
> > like hard drives) are subject to failure at any 
> > time.
> 
> Actually, most "electronics" (as distinct from
> electromechanical devices -- like hard drives)
> exhibit a bathtub curve of failure probabilities.
> They fail soon after manufacture (one edge of the
> bathtub) or "at maturity" (the other end of the
> bathtub).
> 
> This assumes they are used in their proper
> environment (Vcc, Tambient, etc.) -- something that
> isn't always guaranteed in a "PC" case (you'll
> note that a "genuine" server case tends to have
> a sh*tload more fan noise associated with it -- since
> cooling is the number one cause of accelerated
> failures (I think +10C halves MTBF, as a rule of 
> thumb)
> 
> Some devices (notably, newer CPU's with sub micron
> geometries) will have a more predictable "wearout"
> point due to electromigration, etc.  (I've not
> done the math but it intuitively *feels* like
> the number of clock cycles you'll get from a CPU
> is a constant, K, regardless of speed, over it's
> lifetime... this would be an amusing bit of
> research to pursue).
> 
> Other devices (CD-R/W) have similar wearout points
> inherent in their designs (e.g., total PoHr's
> limits usable life).  Remedies here tend to be
> either "difficult" (i.e. independantly control
> power to said device -- easier done for external
> devices) or "practical" (i.e. plan on replacing it!)
> 
> > This is the reason for redundancy, 
> > especially when you bring "backup" into the picture.
> 
> Disks and power supplies are most often made
> redundant.
> Power supplies fail due to their greater stresses --
> they live in a warmer environment (since many are not
> well ventilated) and handle "extremes" (i.e. switching
> currents result in lots of thermal/mechanical shocks
> to these devices at the switching frequency... things
> that their low mass experience more dramatically
> than would be evident outside the package (where
> larger masses prevail).  Capacitors (and connectors)
> tend to be a high failure rate item as well.
> Capacitors can degrade even when not in service
> (store a machine in a hot Tucson garage and you're
> not doing it any favors!).
> 
> Disks nowadays have very high MTBF's (1,000,000
> PoHrs).
> But, most sit in poorly ventilated cases where they
> run a lot warmer than they would like.  You either
> invest in loud fans or redundant data stores
> (note that a power supply/controller failure can
> render a RAID array useless.  And, software bugs
> can hose redundant drives in an ohnosecond -- I
> lost two copies of an archive to a driver bug in
> an old version of FreeBSD  :< )
> 
> Bottom line, if you *really* want to save your data,
> keep it redundant *machines* (so a failure of one
> doesn't kill "both" copies of your data) -- and in
> different locations (so a fire or lightning strike
> doesn't do likewise!)
> 
> I rely on *lots* of spindles (so I only lose a little
> at a time) plus three backups on different media:
> CD-R (which is really NOT very reliable, long term),
> magnetic tape and MO cartridges.  Thankfully, the
> amount of *dynamic* data that I have that would be
> subject to this sort of backup is much less than
> the archive already built  :>
> 
> Last note on connectors... they lurk in often ignored
> locations!  In a modern PC, one of the connectors
> most frequently ignored (for reliability) are those
> for the memory devices (SIMMs/DIMMs/etc.).  The
> quality
> of these vary *immensely* -- and, there is no easy
> way to determine what you've got!
> 
> In addition to tin/gold issues, many of these have
> very low insertion ratings -- some as few as *6*!
> Of course, that doesn't guarantee that it will
> fail on the 7th attempt... but, if you are pulling
> memory frequently, you have to wonder *when* you
> will cross the line from "reliable" to "marginal".
> 
> Tinkerers beware  :>
> --don
> 
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