On Tue 24 Jun 2008 23:11:52 NZST +1200, Nick Rout wrote: > It seems to be taking about 20 minutes This seems far too long. USB > data rate 60MB/s.
Most points have already been made, but never mind. USB is a serial bus, its data rates will therefore always be specified in bits per second. USB 1 is 12Mbit/s, USB 2 is 480Mbit/s. Calculate about 10 bits per byte to be realistic, so I'd treat anything above 50Mbyte/s as an unexpected bonus. For flash cards and sticks the data goes through a number of bottlenecks, the bottom line is as usual the smallest one in sight along the line. The flash memory itself is much faster for reading than for writing, because for writing an erase cycle needs to be performed first on a block of memory cells. You can view flash memory (cards, and certainly USB sticks) as a hard disk, not a DRAM memory module, which has its own controller. This controller performs the erase as needed, access control as appropriate (it's called SD = secure digital for a reason, and the reason is not to ensure you get accesss to the stuff on it - nod content mafia), and also defect management - you might have noticed that flash memory chips always have less than their expected power-of-two capacity, the rest is reserved for defect management. This controller is integrated on the memory chip, and its workings are already included in the speed specified for the chip. Cheap flash stuff is *a lot* slower than high performance varieties. (And often less reliable - aka kiss your photos good-bye.) Then the flash chip gets hooked up to a USB interface chip (which then all goes on a key ring, often with a geeky blue light). Now if you think the combination thereof would give you the max USB can handle, you haven't been nearly cynical enough. Slow 8 bit microcontrollers are cheap, and Joe Henry wouldn't know to ask for speed when in the shop - but oooohh look, it says "8GB" on the pack - wow, that's a lot! Therefore no point for Industry(TM) to give you a fast product. Similar for flash card readers. You will have to spend money very carefully to get a card reader close to the speeds specified for top-end cards (and not all that are expensive deserve their price tag). > 1. USB flash drive cannot handle the data rate, tough one Nick; Yep. Strong possibility. Especially for CheapStuff(TM). > 2. USB operating at USB1.1 rate only. How would I diagnose that? lsusb -v You can restrict its copious output to one specific device (which you locate with lsusb first). Somewhere in their it says what USB level the device is operating at (and which driver is being used). > dmesg displays a lot of lines with the term USB in them, dunno whats relevant. Probably nothing much, though if it says the driver it might be possible to deduce the speed (something like ehci = USB 2, uhci = USB 1). Volker -- Volker Kuhlmann is list0570 with the domain in header http://volker.dnsalias.net/ Please do not CC list postings to me.
