A typical MTBF for EISD hard drives is 500,000 hours. However, this is just
a statistical benchmark figure used by manufacturers. It is NOT a guarantee
by any means.
73, Keith NM5G
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of David Kirkby
Sent: Sunday, September 11, 2005 7:16 PM
To: David Lisney
Cc: amps@contesting.com
Subject: Re: [Amps] Screen Supply for 4CX250 series
David Lisney wrote:
> Hi, a couple of people emailed me off list for the circuit diagram of
> my transistor stabilised screen supply, sorry I had a hard-drive
> failure (how do they possibly claim such amazing MTBFs)
The MTBF's on hard drives are quoted in an odd manner (well odd to me
anyway), but I guess it has some logic to it.
A decent SCSI hard drive will have an MTBF of over 1 million hours, but this
does *NOT* mean if you take a load of hard drives and run them until they
break, the mean time before failure will be 1,000,000 hours
(114 years)
The MTBF is based on the mean time for a random failure to occur, assuming
that you replace the disks periodically in a preventative maintenance
schedule. You need to replace them at the end of their service lives (5
years typically for SCSI, less for other disks), even if the disks are still
working.
So if the service life of a disk is 5 years and the MTBF is 114 years, you
will (on average) need to replace the disk 22 times over before a random
failure will occur that will mean a disk fails under 5 years old.
Of course, few of us bother replacing disks that are not broken, which is
why we don't see average lifetimes close to the MTBF's.
If you make heavy usage of disks (lots of DVD ripping or similar) then SCSI
are a lot better. I knew someone who was hammering IDE disks very hard 24
hours/day. These would often fail three or four times during the 3 year
warranty period. I suggested he switched to SCSI, which he did and has not
looked back. They are built much better, and have more intelligent drive
electronics that minimises head movement. Of course, the downside is that
they are 2 or 3 times more expensive for the same capacity.
--
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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