Tape drive read speed

[Joaquin Martinez_1]

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]

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.

[Joaquin Martinez_1]

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.