--- Steven Hartland <[EMAIL PROTECTED]> wrote: > From: "Patrick Proniewski" <[EMAIL PROTECTED]> >> # dd if=/dev/ad4 of=/dev/ad6 bs=1m >> >> It yields to poor performances: >> > That's actually pretty good for a sustained read / write on a > single disk. > Does somebody know, why this is "pretty good"? I mean: Where is the bottleneck?
As far as I know, SATA is quite fast... And memory to memory copies are quite fast... disc<->memory should be quite fast, too. >> Is it normal that data rate won't go upper than 35/38 MB/s ? >> Hmm... Can u find out, if DMA transfers are enabled for those discs? What does dmesg say? What does "sysctl hw.ata.ata_dma" say? Maybe atacontrol(8) says something useful about SATA discs, too (e. g. atacontrol mode 0)? Can u try the following commands, when the system (especially the discs) is idle? #dd if=/dev/ad4 of=/dev/null bs=1m count=1000 #dd if=/dev/zero of=/dev/null bs=1m count=1000 (Maybe you could find a way to copy /dev/zero to /dev/ad6 without destroying the previous work... :-)) E. g.: # dd if=/dev/ad6 of=/tmp/arne bs=1m count=1000 # dd if=/dev/zero of=/dev/ad6 bs=1m count=1000 # dd if=/tmp/arne of=/dev/ad6 bs=1m count=1000 ) > one more question: is dd(1) a good way to duplicate a boot > drive to make a bootable spare disk ? > I say, is the file system on /dev/ad4 read only during the "dd"? If /dev/ad4 changes before "dd" completes, ad6 might need a fsck or ad6 might be useless... Btw.: I use gmirror(8)... But then an unintentional, fatal change von ad4 would be fatal for ad6, too... :-)) So I have to hope, that I do not type things, I shall not type (luckily I have some boot CDs for that unlikely case ;-)) )... -Arne __________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.com _______________________________________________ freebsd-performance@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-performance To unsubscribe, send any mail to "[EMAIL PROTECTED]"