On Mon, 2010-03-08 at 12:16 -0300, Luigi Castro Cardeles wrote: > Hi list and Patrick, > > > the default max_sectors is 240. I change this to 1024 like you said > but the problem continue. > > > If i try the speed: > > > time dd if=/dev/sdc1 of=/dev/null bs=1M count=5 > i get that speed: 972 MB/s > > > but if i run rsync, the upload transfer rate is very slow ( begins at > 4MB/s and goes below until 0.7KB/s) [Please don't top-post on this list] First of all, is this device a real hard disk, i.e. a mechanically rotating magnetic surface, or is it some kind of Flash drive? If it's the latter, then read on. I've been looking into this recently because of wildly varying performance when writing to a pendrive. It turns out that Flash memory isn't "really" random access when it comes to writing (reading is OK though). Quick summary: The Flash technology only allows writing zeroes, not ones, and is organized in blocks of say 128 or 512 bytes (this varies according to manufacturer) so to write some binary data in the middle of an existing block the procedure is: 1) Read the entire block to some short-term scratch memory 2) Reset the block to all 1's. 3) Modify the scratch memory with the new bits 4) Copy the 0 bits of the scratch to the Flash block (all this happens inside the drive of course; AFAIK it's not visible even at the level of the kernel driver). This process takes a very long time, and when you're repeatedly writing small amounts of data (e.g. to update a directory) it all has to be done multiple times, even for the same drive block. A few days ago I copied a 2GB file to an existing VFAT filesystem on an 8GB pendrive, reputedly one of the fastest on the market. It took over two hours. I then tried just simply copying the data directly to the drive using 'dd' (i.e. no filesystem). It finished in under 5 minutes. BTW, rsync is a killer on these drives because it adds another layer of reading and hashing. In this particular case it's a false economy. 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
