Re: dd(1) performance when copiing a disk to another

From: Arne (arne_woerner_at_yahoo.com)
Date: 10/02/05

  • Next message: Eric Anderson: "Re: dd(1) performance when copiing a disk to another" 
    Date: Sun, 2 Oct 2005 10:04:46 -0700 (PDT)
To: Patrick Proniewski <patpro@patpro.net>

    Hi!

    --- Patrick Proniewski <patpro@patpro.net> wrote:
    > > Can u find out, if DMA transfers are enabled for those discs?
    > > What does dmesg say?
    >
    > see end of mail for full dmesg output,
    >
    Looks good... :-)) But I never saw FBSD's kernel messages about
    SATA drives... ;-)

    > > Maybe atacontrol(8) says something useful about SATA discs,
    > > too (e. g. atacontrol mode 0)?
    >
    > # atacontrol mode 0
    > Master = BIOSPIO
    > Slave = BIOSPIO
    >
    Hmm... 0 seems to be the wrong ata... Thats why the output does
    not fit to SATA drives, I think...

    > # dd if=/dev/ad4 of=/dev/null bs=1m count=1000
    > 1000+0 records in
    > 1000+0 records out
    > 1048576000 bytes transferred in 17.647464 secs (59417943
    > bytes/sec)
    >
    That seems to be 2 or about 2 times faster than disc->disc
    transfer... But still slower, than I would have expected...
    SATA150 sounds like the drive can do 150MB/sec...

    As far as I know, SATA busses are independant from each other (no
    master/slave; every drive gets its own cable)... Maybe "dd" cannot
    issue a read request, while the write isn't completed? DMA
    shouldn't be the problem, since the memory interface is quite fast
    in your case...

    So there remain the questions:
    1. Why does the read speed drop in ur setting (maybe writing to
    ad6 takes more time than reading from ad4? u could try to run two
    dd processes one with if=ad4 and the other with if=ad6)?
    2. Why can't we reach 150MB/sec?

    > > (Maybe you could find a way to copy /dev/zero to /dev/ad6
    > > without destroying the previous work... :-))
    >
    > well, not very easy both disk are the same size ;)
    >
    I thought of the first 1000 1MB blocks... :-)
    The write speed might be interesting...
     
    -Arne

                    
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  • Next message: Eric Anderson: "Re: dd(1) performance when copiing a disk to another"

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