Date: Thu, 08 Jul 1999 15:46:14 -0700 From: The Clark Family <Clark@open.org> To: jsd@gamespot.com Cc: freebsd-questions@freebsd.org Subject: Re: HP T4000s Tape Drive problems Message-ID: <199907082224.PAA27583@opengovt.open.org> In-Reply-To: <199907082054.NAA03455@hudsucker.gamespot.com> References: <199907080218.VAA14937@hostigos.otherwhen.com>
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From what I remember: Order that the equipment came out (from my vantage point): DDS-1 DDS-2 Exabyte (DAT) DLT (4000) DDS-3 DLT (7000) This email is not intended to be a "standalone" communication, it probably won't make much sense without a few emails passing back and forth. DDS-1 was the first tape format I was exposed to that wasn't based on QIC (Quarter Inch Casette) technology. (Its based on a 4-mil derivative of DAT and uses a helical-scan technology, like VCRs.) QIC has paseed into the "attractive nusance" stage. I liked DDS-1, because it was fairly fast, fairly high capacity, and not terribly expensive. I think we were getting the bare mechanisms from HP for about 500$ (US) each. (2GB capacity, 4GB with compression, I think.) DDS-1 had one disadvantage, we couldn't run any of the drives for more than three years (nightly backups) without them wearing out. DDS-2 was the tape format preferred by the UNIX heads at our shop. It was very similar to DDS-1 (used the same tape), but featured hardware based data compression. (4GB only) On UNIX, where the backup software was the definition of primitive, hardware compression was the only type easily available. The hardware compression, and the fact that the UNIX guys bought from higher priced VARs, made the DDS-2 stuff quite a bit more expensive. Maybe 1k$ (US) per drive. I seem to remember that Exabyte jumped into the fray at this point. Their drives were based on 8-mil DAT technology, and because they had more surface area, they had a higher capacity. I had a SunOS running friend that had exclusively Exabyte. I tend to see exabyte drives in Sun shops. I think Exabyte was trying to appeal to the elitist part of the UNIX user. And to a degree, I think they succeeded. I can't argue that the Exabyte drives are or are not worth the extra money. I also can't argue that the drives aren't better. *BUT* DLT fell into my lap before I had to face the issue. I was on the PC side of the house, when the UNIX guys were talked into buying their first DLT drive. Lets just say that their favorite sales rep had more sex appeal than brains. She sold them a DLT4000 patched to appear as a Exabyte 8505XL. Why would anyone do such a thing? Because HP hadn't built in support for anything bigger than an Exabyte 8505XL into HP-UX at that point. To get drivers for a DLT4000 required that you buy the HP branded version of the DLT4000. No one knew that yet though. (Closed vendor hardware support sucks! Long live semi-open platforms!) Of course, that whole mess didn't work. I was able to get the drive from them, just to let them save face. They ended up buying a HP DLT4000 instead. Once I was able to re-configure the DLT4000's firmware to show what it really was, I was able to put it into use. (Took some serious VAR abuse to get the correct tools.) I should say, at this point, that the reason for the evolution of tape drives, is that the servers that they are asked to back up are growing continually larger. Consequently, to avoid using several tapes to do a full backup, we were in need of a two fold increase in tape capactiy almost every six months. DDS-1 -> DDS-2 -> Exabyte -> DLT4000 -> DLT7000 There are at least three advantages to DLT. One, is the increase in capacity. The native capacity of a DLT4000 tape is 20GB. Compressed is 40GB. That is enough to handle most systems full-backup needs with one tape. (RAID arrays.) Second, is their speed. I don't remember the numbers off the top of my head, but 20MB / second seems to ring a bell. Third, is the fact that they use a relatively low-tech approach to tape utilization. In other words, they don't (seem to) suffer the wear out problems that I've seen with helical scan tape drives. Comparing the MTBF numbers, and my personal experience with helical scan tape drives, I wouldn't be supprised to see DLT drives work for 10years. (Hopefully they'll be obsoleted though.) DLT does also have some pitfalls: One, is that they are expensive. I seem to remember that it was usual for the DLT4000 to go for about 4k$ when the first came out. Second, is that it takes quite a while for the tapes to load load and unload. This can be a problem in tape jukeboxes, or if you tend to need bits of data off the tapes often. Third, is that they really belong on a UPS, and with operators who are not idiots. We had a problem with a unit that was repeatedly power cycled, while in use. Because of the complexity of the tape pickup spool, it is possible to get a tape stuck inside, (if an idiot has access to the drive). Removing a stuck tape can require a dissasembly of the unit, and is not for the mechanically dis-inclined. (Getting rid of the idiot is a good idea also.) DLT7000 is very similar to the DLT4000, differing in having a more complex way of putting the tracks on the tape. More tracks on the same tape, means higher capacity. 35GB uncompressed, 70GB compressed. There are some 12/25GB Sony AIT drives out ther too. They are supposed to have faster seek times, and nifty feature like memory-in-casette. They would seem to be great drives to base tape-jukeboxes on, but I haven't had a chance to try them myself. Hope that helps. [RC] At 01:54 PM 7/8/99 -0700, you wrote: >>I've resolved backup problems in several shops by just ditching the >>Travan drives. These weren't the cheapos, they were the >>"professional" NS-8 and NS-20 series drives. > >Based on what you and a few others have said about general Travan >crappiness, I will follow your advice and put this thing back in >the cupboard from whence it came, and instead play around with >this Exabyte 8500 I found. > >On a somewhat related note, does anybody have any strong preferences >between DAT/DLT/Exabyte? I'm interested in all experiences, good or >bad... Let me know. > >-- >Jon Drukman >Director of Technology >GameSpot > > >To Unsubscribe: send mail to majordomo@FreeBSD.org >with "unsubscribe freebsd-questions" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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