On Fri, 2012-03-23 at 13:53 -0400, Jeff Wasilko wrote: > On Fri, Mar 23, 2012 at 06:01:35PM +0100, Conrad Wood wrote: > > on storage: > > dd if=/dev/zero of=volume bs=1M : ~ 1,600MByte/s > > cp file1 file2 : ~ 300MByte/s (both files on same volume) > > > > on server > > dd if=/dev/zero of=volume bs=1M : ~ 1,100MByte/s > > cp file1 file2 : ~ 30MByte/s (both files on same volume) > > > > Happy with the dd, but it always drops to a tenth of the performance > > when I do it with cp. > > cp doesn't use large blocks so you'll always get better performance with > dd. Try using dd with bs=4k or 32k and see how it stacks up. > > The coreutils that RHEL ships is pretty old and still uses 4K I/O. We > upgraded to coreutils-8.13 which uses 32K blocks and it helps with > performance. >
dd with 4k still shows 680MByte/s. tbh I would expect the scheduler to merge it together in sequential writes anyways. I didn't find any pattern that exhibits this slow speed apart from copying the file within the same volume. In fact copying a file from ram on to this volume is 700+ Mbyte/s too. I always unmount the volume after copying, just to make sure it really is the diskspeed I am looking at not the server cache. I include the time it takes to unmount when I calculate the speed. Conrad _______________________________________________ Tech mailing list [email protected] https://lists.lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
