Home RAID question

[Josh Coates]

[snip a bunch of talk about why disks fail, blah blah..]

a quick hard drive failure primer:

ATA drives have a MTTF (mean time to failure) rate of between
500,000-1,000,000 hours, and SCSI drives have lots more.  some manufacturers
publish these, some don't - but when they are published, typically they
don't include what's referred to as the "duty-cycle", which is basically the
percentage of time that the disk is 'active' in the context of their MTTF
ratings.

ie. if you have a disk with an MTTF of 500,000 tested at a 100% duty cycle,
then it's equivalent to a 1,000,000 MTTF tested at a 50% duty cycle.  (and
no, they don't actually run them for 500,000 hours..)

the three things that kill disks: usage, heat, dust (no, disks aren't vacuum
sealed), vibration

aside from usage, the most important one is operating temperature (factoring
in the arrhenius curve - w00t, i found an excuse to use the name of a dead
swedish guy) and ambient temperature.

and then you put these things into a bath tub curve, you get negative aging
(infant mortality) and positive aging (wear-out) but in the base of the tub
you usually end up with a failure rate of 1-2% per year.

power supplies killing disks?  um... never heard of any data supporting this
- it's usage, heat, dust and vibration.

-josh

> -----Original Message-----
> From: plug-bounces at plug.org [mailto:plug-bounces at plug.org] On 
> Behalf Of Gregory Hill
> Sent: Thursday, May 11, 2006 1:47 PM
> To: Provo Linux Users Group Mailing List
> Subject: RE: Home RAID question
> 
> I'm going to have to assume you work in an IT department or something.
> I haven't RMA'd a hard drive since the big IBM fiasco about 5 
> years ago where they released a ton of faulty drives.  I've 
> had dual WD 74GB Raptors in RAID0 for about 2 years with no 
> problems (using an onboard promise sata raid controller, then 
> the nvidia sata raid controller after that).  I've probably 
> only RMA'd 3 or 4 hard drives in my life.  Come to think of 
> it, I haven't had to RMA a hard drive since I started buying 
> good power supplies.  Do you use the cheapo ones?  If it came 
> with the case, then the answer is almost always yes (though 
> there are a very few rare occurrences of cases coming stock 
> with quality power supplies).
> Would be interesting if there's a correlation there.
> 
> Greg
> 
> > -----Original Message-----
> > From: plug-bounces at plug.org [mailto:plug-bounces at plug.org] On Behalf
> Of
> > Corey Edwards
> > Sent: Thursday, May 11, 2006 1:30 PM
> > To: plug at plug.org
> > Subject: Re: Home RAID question
> > 
> > On Thu, 2006-05-11 at 13:22 -0600, Andrew McNabb wrote:
> > > RAID 5 makes it so that a single disk can die without having to
> restore
> > > from backups.  However, it's always possible that two will die at
> about
> > > the same time.  This is especially true if your disks are from the
> same
> > > lot, or if it takes several weeks to replace a disk.
> > 
> > Or if the disks are in the same computer and you get a 
> power spike. I 
> > just want to emphasize how common it actually is to lose 2 disks at
> the
> > same time. Not every day, certainly, but it's happened to me
> personally
> > twice in the last two years. In that same period of time I've RMAd 
> > probably 10 other drives for single failures.
> > 
> > Backups, backups, backups!
> > 
> > Corey
> 
> 
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