Date: Mon, 30 Dec 1996 10:48:48 +0000 From: Simon Reading <aat81@dial.pipex.com> To: grog@lemis.de, se@freebsd.org Cc: freebsd-hardware@freebsd.org Subject: Are HP DAT drives more unreliable than others? Message-ID: <3.0.32.19961230104539.00695500@pop.dial.pipex.com>
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Hello, In the freebsd-hardware mailing list, there has been an ongoing thread wrt DDS reliability. I think we may gain some useful info from posting to comp.sys.hp.hardware. Questions which we are trying to answer include: - How reliable is DDS/DDS-2 (DAT) technology? - Is any one brand of DDS drive better or worse than another? (or 'Do the HP drives warrant their Freebsd warnings?') - Can anything be done to extend DDS drive life? - Is there a common failure mode for DDS? This was prompted by the following warning, reported in http://www.freebsd.com/handbook/handbook125.html#267: >Hewlett-Packard HP C1533A . . >Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 2 of these drives. Neither lasted more than 5 months. >From mail that I have received I believe that the DDS mechanism, or more precisely the head, wears out and break down. The questions we're particularly concerned with are 1. How does the head wear out? and 2. Are HP DDS2 drives any worse / better than other DDS2 drives (eg. Sony SDT 7000)? Greg wrote: >Stephen Esser wrote: >>> Greg wrote: >>> My DAT worked fine >>> initially and then gradually faded, getting more and more read/write >>> errors as time went on. >> >> But the head drum is generally not covered by warranty, since >> its useful life is typically in the 1000 to 2000 hours range. >> (Some 1000 8GB (compressed) backups at full speed, or 300 at >> 33% of the nominal streaming data rate !!!) > >This, again, is interesting information for a number of reasons: > >1. I haven't seen any information that the drum isn't covered. Maybe > I just forgot it. Unfortunately, I can't find any warranty > information. > >2. The time you quote is *horribly* short. How can this compare with > the documented MTBF. According to HP, the MTBF for the 35470A is > 50,000 power-on hours, and the MTBF for the C1533A is 200,000 > power-on hours. In each case, they're assuming a duty cycle of > 12% (which I exceed), so the real MTBFs would be 6,000 operating > hours for the 35470A or 24,000 operating hours for the C1533A. > > My backups typically write a whole tape and take about 8 hours per > day. Tonight's backup started at 9 pm and finished (after a > verification read) at 5:07. That's a 33% duty cycle, which would > have the 35470A die after about 2 years. > > If we took your figures, they should die after about 4 to 8 > months, which is pretty much my experience. The only thing is, > this is the first I have heard of the figures. There's nothing in > any documentation I've seen which suggests that the drum is a > high-wear component. Laser printer documentation does indicate > that the print drum requires frequent replacement, for example. Q. can anyone confirm the life of the head drum? (Please state the source of this info). Q. Typically, how expensive is it to replace an HP head drum? Q. How does the reliability of HP compare to other makes of drive? It would be useful if replies regarding drive experiences include: 1. Make, model 2. Date of purchase (or manufacture) 3. Reliability and duration of ownership. 4. How heavy usage the drive gets. Simon PS. We've elimated cables, termination, tape conditioning (operating temperature, retensioning, ..), tape type etc. as a source of our problems.
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