From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Stan Bischof Newsgroups: gmane.emacs.help Subject: Re: dd - unequal speed from partition to partition, partition to file, file to partition Date: 28 Mar 2011 19:37:52 GMT Organization: Sonic.Net Message-ID: <4d90e390$0$10613$742ec2ed@news.sonic.net> References: <25819901-c857-405d-8ef6-ee0ac2ee1ea0@18g2000prd.googlegroups.com> NNTP-Posting-Host: lo.gmane.org X-Trace: dough.gmane.org 1301343546 23783 80.91.229.12 (28 Mar 2011 20:19:06 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Mon, 28 Mar 2011 20:19:06 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Mon Mar 28 22:19:02 2011 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Q4Itx-0007yI-SU for geh-help-gnu-emacs@m.gmane.org; Mon, 28 Mar 2011 22:19:02 +0200 Original-Received: from localhost ([127.0.0.1]:37350 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Q4IdV-00052B-JO for geh-help-gnu-emacs@m.gmane.org; Mon, 28 Mar 2011 16:02:01 -0400 Original-Path: usenet.stanford.edu!news.glorb.com!news2.glorb.com!news-xfer.nntp.sonic.net!posts.news.sonic.net!nnrp1.nntp.sonic.net!not-for-mail Original-Newsgroups: comp.os.linux.misc,comp.unix.shell,comp.lang.c,gnu.emacs.help Original-Followup-To: comp.os.linux.misc User-Agent: tin/1.9.3-20080506 ("Dalintober") (UNIX) (Linux/2.6.26-2-686 (i686)) Original-Lines: 40 Original-NNTP-Posting-Date: 28 Mar 2011 19:37:52 GMT Original-NNTP-Posting-Host: 9bb18459.news.sonic.net Original-X-Trace: DXC=kjQNdT::0D4JjN; Mj63oH7m4K\QM1CV^01OYf0H`?; X1Y:ij7iBS109lRh5[igSQY=be>AJL=]Ih1 Original-X-Complaints-To: abuse@sonic.net Original-Xref: usenet.stanford.edu comp.os.linux.misc:801753 comp.unix.shell:250064 comp.lang.c:994158 gnu.emacs.help:186363 X-Mailman-Approved-At: Mon, 28 Mar 2011 16:01:10 -0400 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:80492 Archived-At: In comp.os.linux.misc bolega wrote: > dd - unequal speed from partition to partition, partition to file, > file to partition > > /dev/sda1 to /dev/sda2 around 25Meg/s > /dev/sda1 to a file_sda1 around 12Meg/s > file_sda1 to /dev/sda1 around 5Meg/s > > Why ??? > > I have played with various block sizes such 1M, 4M, 500M > > In the all three cases, its from the same disk to itself OR from > different disks, eg SATA to USB ... if I recall correctly. > > Please give an explanation why read from a file to disk partition is > so slow ??? > Well, the obvious answer ( maybe even the right one ! ) is that different disks and interfaces have different speeds available, different cache sizes and so on. Transferrring from one SATA disk to another SATA on the same bus will definitely be a different speed than transferring from the same disk to another disk mounted on USB. Transferring from one disk to another will be different ( likely faster ) than from one disk to elsewhere on the same disk. In each case the data goes through a path- and the slowest link in that path will determine the overall speed. Then you get into other items like cache size- small files may be very fast if they fit into cache while big files can be much slower since they overflow the cache. Lots of variables. There is absolutely no reason to expect the various paths to be the same speed , not even taking into account the software used. Stan