Hi Neha, On Apr 11 2013, neha naik wrote: > HI Greg, > Thanks a lot. Everything you said made complete sense to me but when i > tried running with following options my read is so slow (basically with > direct io, that with 1MB/s it will just take 32minutes to read 32MB data) > yet my write is doing fine. Should i use some other options of dd (though i > understand that with direct we bypass all caches, but direct doesn't > guarantee that everything is written when call returns to user for which i > am using fdatasync). I'm no kind of expert, but the last time I found myself timing dd, I found that the block size was critical, and 4096 bytes is a very small block size, from a dd point of view. On freebsd at least, cranking it up to at least 1MB did great things for its performance. What happens with "bs=1M" ? > time dd if=/dev/shm/image of=/dev/sbd0 bs=4096 count=262144 oflag=direct > conv=fdatasync > time dd if=/dev/pdev0 of=/dev/null bs=4096 count=2621262144+0 records in > 262144+0 records out > 1073741824 bytes (1.1 GB) copied, 17.7809 s, 60.4 MB/s > > real 0m17.785s > user 0m0.152s > sys 0m1.564s > > > I interrupted the dd for read because it was taking too much time with > 1MB/s : > time dd if=/dev/pdev0 of=/dev/null bs=4096 count=262144 iflag=direct > conv=fdatasync > ^C150046+0 records in > 150045+0 records out > 614584320 bytes (615 MB) copied, 600.197 s, 1.0 MB/s > > > real 10m0.201s > user 0m2.576s > sys 0m0.000s > > Thanks, > Neha _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
