Re: slow tar performance on fbsd5

From: Tulio Guimarăes da Silva (tuliogs_at_pgt.mpt.gov.br)
Date: 08/24/05

  • Next message: Tulio Guimarăes da Silva: "Re: slow tar performance on fbsd5" 
    Date: Wed, 24 Aug 2005 15:00:50 -0300
To: freebsd-performance@freebsd.org

    Hi,
      I´ve got the same kind of problem, not only with DDS-[234] tapes, but
    also with "all-powerful-with-bells-and-whistles" AIT-3 units, with
    controllers ranging from Adaptec stock 2940 to PCI-X Ultra-320... almost
    same results.
      The problems seems to lie in tar itself; I read there´s something to
    do with block sizes, but using -b with larger values got me not much
    more than corrupt or incomplete data. :( The only way I got to have
    decent transfer rates AND reliability was to filter *archiving* through
    dd, including block sizes. For example, to archive:

      # tar -zcpf - /usr/local | dd of=/dev/sa0 bs=64k

    and to restore:
      # tar -b 128 -zxvf /dev/sa0

      The above is particullarly true for remote transfers; if you´re using
    tar over rsh/rmt (-f host:/path), you´ll surely prefer simple "rsh/tar"
    with output redirection. ;)
      Note that block sizes in tar count as 512-byte ones, while in dd they
    can be specified as Kilobytes or even megabytes. Besides speed, there´s
    a sensible boost on storage space when using dd-block-sized transfers.
    The apparent reason for that is tar actually uses -b 20 (10kb) blocks,
    while 10GB+ tapes usually expect larger sizes.
      For AIT-3, I didn´t notice any real good improvement past 128kb block
    sizes; I didn´t experiment enough with DDS-4 because our test tape drive
    got a heart attack and quit... BTW, it returned 2 weeks ago and I didn´t
    give it any attention; it may be a little depressed by now, so I guess
    I´ll return it to test beds. :) Anyway, I wouldn´t try anything lower
    than 32kb blocks on it.
      I can´t remember if I did any test pointing to /dev/null, as mr.
    Hartland suggested, nor from /dev/zero or /dev/random... it´s worth a try.
      I´ll post new results as soon as I get´em (if any). ;)
      Have luck,

    Tulio G. da Silva

    Steven Hartland wrote:

    > Might be silly but do u get similar results if u:
    > 1. expand to a memory backed disk
    > 2. expand to /dev/null
    >
    > Steve
    > ----- Original Message ----- From: "JG" <jarek@adeon.lublin.pl>
    >
    >> I had to unpack a lot of tar archives and I occasional noticed terrible
    >> bad performance on freebsd5.
    >

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