On Mon, 2012-01-23 at 03:25 +0000, Marko Vojinovic wrote: > On Monday 23 January 2012 02:41:07 you wrote: > > Now I'll see how USB is going to work --- a 2.2 GB file is about to be > > written... ;-) > > As a side note --- is it normal to have the write-to-USB-flash speed of > 2.5 MiB/s (on average)? > > I am supposedly using USB2.0 port, and have a 8 GB flash drive. Writing a file > of 2.2 GB in size takes around 15 minutes to complete. Also that KDE progress- > bar thing is reporting the 2.5 MiB/s value (on average) which fits my > calculation, but I was wondering if this is the expected performance or not. I'd say that seems on the slow side, but there are several factors that can affect it. For one thing, not all flash drives are created equal. Even if they're supposed to work at USB2 speed, that's just the bus speed of getting the data across the wire and doesn't really tell you much. Cheaper drives are definitely slower than more expensive ones which have larger internal buffers. Most commercial drives don't have any published info on these speeds, but occasionally one sees comparitive benchmarks being published (e.g. http://usbflashspeed.com/). The other important factor is fragmentation. Even though flash drives are theoretically random-access, the way flash memory works means that a sparse distribution of blocks to be modified can make a large difference to the effective write speed (see http://en.wikipedia.org/wiki/Flash_memory#Limitations). This becomes noticeable if you repeatedly create and delete randomly-sized large files on the drive. In time the drive will become slower and slower because of fragmentation, and it can sometimes make sense to copy the entire contents, reformat the drive and copy the files back again in order to "refresh" it. AFAIK there are filesystem designs which try to minimize this effect, but I assume we're talking about VFAT here, as it's the lowest common denominator for practical purposes. poc -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
