On Sun, Jun 17, 2012 at 7:58 PM, Alan McKinnon <alan.mckin...@gmail.com> wrote: > On Sun, 17 Jun 2012 19:27:36 -0400 > Michael Mol <mike...@gmail.com> wrote: > >> So, I'm using dd to write the Gentoo LiveDVD ISO directly to an SDHC >> card. I was wondering why the transfer rate had slowed from 20MB/s to >> 6MB/s, so I ran 'sudo tail -f /var/log/messages' to see if there were >> I/O errors slowing things down. >> >> What I found was a flood-stream of message blocks that look like this:
[snip] >> ... Any idea what kernel configuration flag I may have enabled to >> cause these to be continually generated? My first guess would be >> something like 'kernel lock debugging'...if that's what I'm seeing >> here, where would I go to file a bug report against the usb-storage >> subsystem? >> > > 6M is what you should expect from a good Class 6 SDHC card, and those > are quite rare in consumer shops (few carry better than Class 4 in my > experience). Yeah, for a given class N, N MB/s is minimum certified transfer rate. Though they probably don't take cover block reflashing in that... > Writes start very fast (it's going into the kernel buffer) > then gradually slow down to the card's actual speed, which is what you > appear to be seeing. That kernel buffer would have been a gigabyte or two in size, and I don't remember noticing that while watching in htop. > > 20M write speed would be a Class 20, which doesn't exist yet :-) Well, more to the point there's no certification level for it. Devices can exceed their certification level. > But what is your actual query? About the write speed? No, not really. TBH, I wasn't expecting to be able to consistently write quickly to the beginning of the card, but slowly at the end; I wanted to make sure the card wasn't going bad given the abruptness of the change. Actually, the more I think about it, I think it happened at the 2GB boundary, where some funky pin logic changes. (And where SD becomes SDHC). So I think that's where the performance shifted. Maybe I'll invest in a bunch of fast 2G cards, if it means the performance is consistent, and I'd still fit just under 200 shots. > > Or about the presence of the messages? Yeah, it's the messages I was curious about. -- :wq
