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Operating System - Tru64 Unix
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Tape drive read speed

Joaquin Martinez_1
Frequent Advisor

Tape drive read speed

Hello all. I've been tasked to restore a logical export of our database we made using tar, on a DLT IV drive mounted in our AlphaServer ES45 running Tru64 V5.1B. I must first say that I am no SA, I have *some* unix/linux knowledge but that's about it, I am a DBA. This export took 5 tapes of 40/80GB capacity and it was done using the exp utility of Oracle exporting it directly to the tape (parameter file=/dev/tape/tape0). I mounted the first tape yesterday morning and started the import process. I was surprised, however, that it took almost a full day for it to ask me for the second tape. Today, I started investigating why this is so.

Using collect -s t, I could see that it is reading an average of 600kb/s (I assume column RKB/S is read kilobytes per second). This traduce to almost a full day to read a tape. This is not desirable. And so I want to ask if this is the normal behaivour I should expect from our drive. By the way, I dont really know the manufacturer of it (though I believe it came with the server). Is there a way to increase this read speed ? (I believe the file was not compresssed at all since we are not using hardware compression device there).

If anyone can shed some light into this, I would really appreciate.

Thank you all!
Ivan Ferreira
Honored Contributor

Re: Tape drive read speed

It's not normal, is a very poor performance but you should not expect more than 1.5/3 MB/s.

I don't know about oracle exports but normally performance can be increased by adjusting the block size.

You can do performance tests with dd for example.
Por que hacerlo dificil si es posible hacerlo facil? - Why do it the hard way, when you can do it the easy way?
Joaquin Martinez_1
Frequent Advisor

Re: Tape drive read speed

Thanks Ivan, I thought the same. At first I thought there should a way to tweek some parameters to increase this speed. I don't know, though I will investigate whether the exp/imp utility let you especify a blocksize, allthough I would believe they use the standard operating system blocksize. I was also thinking the other day to change the device name so to use hardware compression, but I believe this will terribly affect the read speed of the drive once I need it.