Jean-David Beyer <[EMAIL PROTECTED]> writes: > I turned the software compression off. It took: > 524487428 bytes (524 MB) copied, 125.394 seconds, 4.2 MB/s
> When I let the software compression run, it uses only 30 MBytes. So whatever > compression it uses is very good on this kind of data. > 29810260 bytes (30 MB) copied, 123.145 seconds, 242 kB/s Seems to me the conclusion is obvious: you are writing about the same number of bits to physical tape either way. The physical tape speed is surely the real bottleneck here, and the fact that the total elapsed time is about the same both ways proves that about the same number of bits went onto tape both ways. The quoted MB and MB/s numbers are not too comparable because they are before and after compression respectively. The software compression seems to be a percent or two better than the hardware's compression, but that's not enough to worry about really. What you should ask yourself is whether you have other uses for the main CPU's cycles during the time you're taking backups. If so, offload the compression cycles onto the tape hardware. If not, you might as well gain the one or two percent win. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq