DLT IV takes longer than DLT III

[Scott McIntosh_2]

I don't know. You have to tell us what you are doing.

So now it's not 3-3.5 hours to do a tar -cvf, but to do a tar -cvf followed by a tar -tvf? Or a tar -xvf?

You might want to just download hptapeperf for HP-UX and run that against your tape drive with the two different tapes. I don't find your backup scenario to be a valid test of tape drive baseline capabilities.

It might be true that a DLT 8000 drive is "too good" for your incoming data stream vs. a DLT 4000 drive (the basic specs you are performing at with a DLT IIIXT card), but first determine if you are getting correct performance from the drive first.

http://h10025.www1.hp.com/ewfrf/wc/genericDocument?lc=en&cc=us&docname=lpg50460#N10A0D

Thanks,
Scott
HP Support

[A. Clay Stephenson · Accepted solution]

I think I can explain this. The fundamental problem is that you are using a singly-threaded application (tar,cpio) to feed a fast drive. What you need to realize is that when a DLT is not being fed fast enough to stream, it must write a bit, rewind, and write a bit more -- taking about a 100X performance hit as compared to a streaming device. Even though a slower tape drive may be 4-5X slower than the faster DLT in streaming mode, the very fact that it is slower allows it to stream more and thus avoid the huge 100X performance hit more often than its faster counterpart. This is actually a case of less is more. The solution is to run a multi-threaded backup with multiple reader processes to fed the drive at a faster rate. Fbackup is one possible solution; OmniBack / DataProtector is another.

[Robert Milne]

Thanks for your answers..

Yes we are running a simple TAR backup, the reason for this is because of its portability..

And yes we are running a TAR -cvf followed by a readout of tape TAR - -tvf

Thanks for your response Clay, i think your on the right track. I am aware that FBackup is alot more efficient than TAR, but we would rather not run this.

I think FTIO is a multi threaded backup type, and its backwards compatible with CPIO (Which is nice for portability.

I will try this and let you know the results..

Chris