On Wednesday 04 Jul 2007, Chris Dennis wrote:
> Peter Salisbury wrote:
> > Hi,
8<
> > On top of this, I only get 1MB/s with a udf file system on the
> > DVD-RAM and the Linux udf system won't handle a file over 1GB.
> > When I put an ext2 file system on the DVD-RAM the average
> > transfer speed falls to 0.7MB/s.
> >
> > Is it really this bad? Has anyone had a better experience of
> > DVD-RAM?
> Hello Peter
>
> I use DVD-RAMs for backups via Amanda, which reports a write speed
> of about 1100KBps on Panasonic '2-3x speed' discs.
>
> A quick test:
>
> $ time (dd if=/dev/zero of=/media/dvdram/2G bs=4096 count=524288;
> umount /media/dvdram)
> 524288+0 records in
> 524288+0 records out
> 2147483648 bytes (2.1 GB) copied, 958.001 seconds, 2.2 MB/s
>
> real 22m49.100s
> user 0m0.108s
> sys 0m3.132s
>
> shows a throughput of 1.5MBps including the time to unmount the
> disk. gkrellm was showing a transfer rate of about 1.5MBps while
> that was running.
>
> I don't know if DVD-RAMs are supposed to run faster than that or
> not.
Thanks Chris,
I've reformatted the DVD-RAM disk to fat32 and that seems to be the
best performing of {ext2, udf, fat32} (can't believe I'm saying
this!) coming in at about 1.5MB/s for a 100MB transfer. That seems to
tally closely with your Amanda experience so I guess that's just the
way it is.
That's about 37.5% of the advertised performance of the setup. Ah
well...
In case anyone isn't put off DVD-RAM and wants to format the disks for
fat32 there is a small hurdle in that you get this warning:
unable to get drive geometry, using default 255/63
so you have to specify quite a few parameters to get a mountable file
system:
mkdosfs -I -F 32 -s 128 -S 2048 /dev/hdx
(the -s 128 was just a guess but it WFM!)
HTH, Peter
