On Wednesday 21 February 2007 06:42:19 am Joachim Schrod wrote: > Joachim Schrod wrote: > > David Brodbeck wrote: > >> Sure. As anyone who's ever had a couple of hard disks fail can attest, > >> MTBF numbers are mostly fiction. > > > > Well, I can attest that you don't seem to know much about statistics. > > ;-) ;-) > > > > At one of my customers, 10,000s of disks are in use at the servers. > > There MTBF numbers are reliable indicators of how much disks one has to > > buy in advance to exchange the defect ones. > > For the record, I should add that one needs to collect MTBF numbers > (actually, MTTF and MTTR numbers) onself. Data from other > organizations is not reliable, the variance seems to be quite high. > > Therefore, this may be only of use for large installations, and not > for SOHO or mid-sized environments that are probably most common on > this mailing list.
Joachim has a valid point. Though this may be off-topic, I felt it important to state: In our data center, we have 4 EVA 5000 machines each with 168 physical drives. The drives range in size from 72GB to 300GB. We use MTBF in order to calculate our drive replacement costs for these machines. So far we're only replacing about one drive per month. The oldest EVA is roughly five years old. Now, the data center is climate controlled and entirely supplied by redundant UPS units. In addition we have a diesel generator for backup. The generator gets tested at least twice a year to ensure it kicks in. IOTW, the power never goes off and the temperature does not go above 65f/18c. OTOH, I remember getting a call in the early '90s from one of my then-clients. She ran a stationary store in Beverly Hills and her Novell 3.11 server was failing. When I got onsite, I found her mirrored 500MB drives were overheating due to the amount of dust encasing the drives and choking the fans on her DX/66 server tower. The server was enclosed in a closet in a back room of the store and had only been there less than a year. In other words, MTBF is an estimate one can use for professional data centers and is actually fairly reliable when the drives are appropriately used. -- kai Free Compean and Ramos http://www.perfectreign.com/?q=node/46 -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
