topic Re: DAT versus DLT in Operating System - HP-UX

DAT versus DLT

Peter Brimacombe — Wed, 23 May 2001 13:06:54 GMT

we just got a new DLT tape drive with the autochanger. Using OmniBack, the DLT system backs up two K servers and three L servers really fast but we also have an old 700/735 workstation with a 10 mb ethernet card and an 18 Gb file system.

Using our old DDS3 DAT drives or the new DLT drive it still takes 5 hours to backup the 18 Gb file system - obviously the 10 mb ethernet card is the limiting factor. We plan to move the file system to one of the K servers with a 100 mb ethernet. The question is what to do in the interim - the way I understand the DLT tape it streams and data is thrown on it as the data is available, if there is no data then the DLT tape stops, waits , backs up a little and then starts streaming again. I am afraid that over a five hour period there will be alot of wear on the tapes. The DAT drives stream too but their speed more closely matches the speed of the 10 mb ethernet card.

opinions?

Re: DAT versus DLT

Patrick Wallek — Wed, 23 May 2001 13:30:39 GMT

It is true that the stop-backup-restart that the DLT will do is probably hard on the tape, I don't think it will really hurt anything. I would say just go ahead and do your backups as you have been, and try to get the data moved off of the older machine as quickly as you can. Your 10Mb ethernet is one limiting factor. The machine itself may be another. Since it is an older machine it may have problems trying to keep the data going out.

I don't know that there is a lot you can do at this point, unfortunately.

Re: DAT versus DLT

paul courry — Wed, 23 May 2001 13:36:35 GMT

Perhaps you should consider that should you need the data restored the DLT tapes have an error rate that is better by about 2 orders of magnitude than DDS.

Re: DAT versus DLT

Stefan Farrelly — Wed, 23 May 2001 13:50:05 GMT

Weve been running remote backups on DLTs for years without any noticeable increase in tape wear-outs at all. I dont think its an issue.

Re: DAT versus DLT

Dave Wherry — Wed, 23 May 2001 13:53:16 GMT

Peter,
You and the others pretty much covered the situation. A slow workstation with a slow NIC backing up 18GB over the network simply equals a long backup. A faster NIC is all that is going to help you on this workstation. However, you said you are going to move the file system to another server so it ends up just being a temporary inconvenience. No need to spend money on that workstation.

You had a concern about wear and tear on the tapes because of the frequent repositioning. That's called shoe shining and is indicitive of not pushing enough data to that drive. It confirms the slow data transfer rate. As for the wear on the tapes, I don't think that is an issue. I can't remember the specifics, but the service numbers on DLT tapes are really high. When we got our first DLT drive we calculated that we would use a tape for about 5 hours a night, every 3 weeks. With that rotation we could use the tape for about 20 years. It should be rare for a DLT tape to wear out.

Dave

Re: DAT versus DLT

Tommy Brown — Wed, 23 May 2001 14:01:18 GMT

Peter, I have moved the slow system to the top of the session, if it is in the same session as other/faster systems. This allows the DLT to stream and still picks up the other systems reasonably well.
Tommy