On Fri, Jan 15, 2010 at 05:46:12AM +0100, Peter Stuge wrote: > sascha wrote: > > > SATA SSD seems to cost same as USB memory sticks. > > > > its about 30% more expensive > > Ouch. I was looking at really expensive USB memory. > > > > > USB is widely available, but still a serial bus, so only a single > > > request to a single memory stick per host controller is in flight at > > > any one time. (Even with 8 USB ports it's still one controller.) > > > > tests show otherwise: > > single usb stick: > > Results: 967 seeks/second, 1.03 ms random access time > > > > 3 usb sticks on a hub accessed concurrently: > > Results: 907 seeks/second, 1.10 ms random access time > > Results: 916 seeks/second, 1.09 ms random access time > > Results: 915 seeks/second, 1.09 ms random access time > > On the wire there are 1ms timeslots (called frames) that can each be > used for communication with different devices. I expect the seek to > be near-nop in the device so this measures the minimum USB RTT.
if that were the case you would see 300 seeks/second for the concurrent access or more than one request is active on the usb bus. > > It gets worse when transfering data - how bad depends on burst size. > What size are reads(?) between two seeks? USB has lots of layers and > if the bursts are very small then overhead is expensive. 512 bytes _______________________________________________ A51 mailing list [email protected] http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51
