Re: cdrecord: DMA speed too slow
> > cdrecord: DMA speed too slow (OK for 8x). Cannot write at speed 10x.
> > Starting to write CD/DVD at speed 10 in real TAO mode for single session.
> >After a few minutes i stopped the reading process at hdd and cdrecord began
> >to report speeds of 10.1x to 10.6x. Average speed was ~ 7x.
>
> So you just verified, that even 8x was not possible ^^^^^^^^^
Actually i wanted to find out wether cdrecord slowed down speed to 8x
by itself. It obviously didn't - which is fine for me.
Average speed 7x was the result of my reading hdd at the beginning
of my test (cdrecord reports 2.2x) and then stopping that (report: 10.2x)
With hampering, the DMA speed measurement reports 8x to 15x and the actual
throughput is about 2x.
Without hampering, the DMA measurement reports at most 4480 kB/s but
the drive reliably shows average DVD+RW throughput of about 5100 kB/s.
(With 10x CD-RW i cannot reach more than about 1500 kB/s, of course)
So there may be a monotonic correlation between cdrecord's measurement and
the actual throughput. But the eventual mapping between them is still to be
discovered.
With unhampered writing, periodic speed reports of cdrecord and growisofs
show speed near the expected maximum. Varying from CD 10.2x to 10.7x
and being steadily at DVD 3.9x.
Any temporary weakness is too short to show up that way.
I looked for the drive's buffer size and found these old lines (all of a35):
Drive buf size : 1204224 = 1176 KB
Drive DMA Speed: 4385 kB/s 24x CD 3x DVD
Drive buf size : 1204224 = 1176 KB
Drive DMA Speed: 4439 kB/s 25x CD 3x DVD
Drive buf size : 2097152 = 2048 KB
Drive DMA Speed: 4480 kB/s 25x CD 3x DVD
Drive buf size : 2097152 = 2048 KB
Drive DMA Speed: 4470 kB/s 25x CD 3x DVD
There seem to be hours when "Drive buf size" is 1176 KB and then for a few
CDs (or empty trays) the size is 2048 KB.
> Looks like bad scheduling behavior from your OS. Cdrecord runs at highest
> possible real time priority. THe OS should give it highest I/O priority for this
> reason......
Can be the cheapo hardware as well. I don't know. If i was a hardware
crafter i would swap the DVD-ROM to hdb and look what happens. But i'm
an uptime fetishist and love my hard disk even more than my CD-RWs.
So i will leave it as it is ... until there is better reason to fiddle.
Whatever, cdrecord-2.01a35 and my old settings seem to work together
fine.
I just wonder what's up with those buffer sizes.
Have a nice day :)
Thomas
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