Why FW800 so slow?

Discussion in 'Apple' started by Király, Oct 30, 2011.

  1. Király

    Király Guest

    Last night I used asr to do a block level copy of one FW800 drive to
    another. It took 4 hrs, 27 minutes to copy 461.18 GB. That's an average
    speed of 28.78 MB/sec.

    Isn't FW800's max transfer speed 100MB/sec? If so, I only got a little
    over a quarter of the max speed. I figured an asr block level copy would
    get much better results than that. If an asr block level copy only gets
    that kind of speed, what kind of usage would better take advantage of
    the 100MB/sec claimed speed?
     
    Király, Oct 30, 2011
    #1
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  2. When done on the same FW800 bus, that is 2 x 28.78 = 57.56 MB/sec.

    You may have 2 FW800 ports on your Mac, but it is one bus.

    A blocklevel copy copies the entire drive, not just the part that is
    used.
     
    Niels Jørgen Kruse, Oct 30, 2011
    #2
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  3. Király

    Király Guest

    OK thanks. It was a 500GB drive, so then I got 61.42 GB/sec. Only 61% of
    FW800's stated maximum.

    So three questions remain:

    1) What if anything can I do to speed it up?
    2) If an asr block level copy can only get 61% of maximum, why?
    3) What kind of operation can get closer to 100MB/sec, if not asr?
     
    Király, Oct 30, 2011
    #3
  4. Király

    Alan Browne Guest

    My 800 on the iMac fried about 6 months ago, so my memory isn't all that
    sharp. IIRC best copy speeds I got were on the order of 35 - 45 MB/s.

    Which ain't bad.

    I just did a disk to disk copy of a 944 MB .avi file in 30.3 s or 31.2
    MB/s. (system disk to iOmega 2 TB).

    Which ain't bad either.

    Same file to Drobo (USB 2): 15.6 MB/s.
     
    Alan Browne, Oct 30, 2011
    #4
  5. Király

    Alan Browne Guest

    Sorry, that @ 400 (FW).
     
    Alan Browne, Oct 30, 2011
    #5
  6. I've never gotten FW800 to anywhere near the speed you're quoting.
    Short of 'doing the transfer by hand' (e.g. writing a kernel level
    program to talk directly to the hardware and handle the transfer), I
    don't know if you're going to get any better performance.
     
    Michael Vilain, Oct 31, 2011
    #6
  7. Király

    dorayme Guest

    How can a fried iMac FW800 bit mess with *your* memory, it
    probably does not even mess with your iMac's memory?
     
    dorayme, Oct 31, 2011
    #7
  8. Király

    Király Guest

    Okay, it's getting even weirder.

    I tried copying the same drive, a 500GB drive with 461GB of data on it
    (92% full), with SuperDuper, which does a file level copy instead of
    the block level copy that asr does. It completed the task in 3 hours and
    21 minutes, a full hour less than asr took to copy the full 500GB.
    That's 38GB/sec, or 76GB/sec if Niels' claim is correct of doubling
    the time if the drives are on the same bus. That's quite a bit closer
    to the 100GB/sec that is claimed for FW800.

    But that blows out of the water what I had been assuming about asr
    block-level copying being faster than file-level copying. I'm going to
    use SuperDuper for everything now.
     
    Király, Oct 31, 2011
    #8
  9. The 6 months can.
     
    Niels Jørgen Kruse, Oct 31, 2011
    #9
  10. Király

    Paul Sture Guest


    ISTR that the Firewire spec allows 2 Firewire drives to do data transfers
    between themselves without going back to the host (can't remember if they
    need to be daisy chained for this). I've no idea if this capability is
    supported by OS X drivers though.
     
    Paul Sture, Oct 31, 2011
    #10
  11. Forget the peer-to-peer meme. It never happened. The only practical
    aspect is TCP/IP over Firewire.
     
    Niels Jørgen Kruse, Oct 31, 2011
    #11
  12. Király

    Paul Sture Guest


    Thanks for that info. I have always wondered.
     
    Paul Sture, Oct 31, 2011
    #12
  13. Király

    Alan Browne Guest

    That would be useful.

    Even more so would the ability to tell my iOmega drive to copy from one
    to the other without going via the host.
     
    Alan Browne, Oct 31, 2011
    #13
  14. Király

    Paul Sture Guest

    Yes, but on seeing Niels' reply I started thinking about the potential
    gotchas, and it could end up being very complex indeed. Fine in the lab,
    not so good in production.
     
    Paul Sture, Nov 1, 2011
    #14
  15. Király

    Király Guest

    Even taking that into consideration, the file level copy was much
    faster. The 500GB drive had only 39GB of free space on it.

    Block level copy (asr) copied 500 GB in 4 hrs 27 minutes (29MB/s)
    File level copy (SD!) copied 461 GB in 3 hrs 21 minutes (38MB/s)

    Even if the drive had been completely full, SD! would have completed
    the task after 3 hrs and 49 minutes, 38 minutes less time than asr took
    to do a block level copy.

    I found it surprising because the man page for asr claims that block
    level copying is faster.
     
    Király, Nov 1, 2011
    #15
  16. Király

    David Empson Guest

    What size are the files involved? asr defaults to using multiple 1 MB
    buffers for its backups. This means it will be reading or writing 1 MB
    at a time.

    If the average size of the files is significantly over 1 MB, SD! may be
    able to back up faster because it is copying in larger chunks, resulting
    in less overhead for issuing read and write commands. (It also has to
    copy information between the directories, which will slow it down
    compared to a simple block copy, so the average file size would have to
    be significantly larger for it to still be beating a block copy.)

    Try increasing the buffer size used by asr.
     
    David Empson, Nov 2, 2011
    #16
  17. Király

    Király Guest

    Aha. These were big honkin' video files. That would explain it.
    Thanks for the suggestion, I make try that next time I need to copy a
    lot of data. Or maybe I'll just forget it and use SuperDuper.
     
    Király, Nov 2, 2011
    #17
  18. Király

    Király Guest

    Niels says that while FireWire may have been designed that way, it
    doesn't really work that way in practice. He says that transfers
    between two FW drives on the same bus do go through twice, which would
    explain my 304Mb/s transfer rate when the theoretical maximum is
    800Mb/s.
     
    Király, Nov 2, 2011
    #18
  19. Király

    Lewis Guest

    You aren't going to gain anything using block copies on a drive full of
    large files. You will gain tons of time if you are doing something like
    copying a boot drive with a full system install and millions (or so) of
    files.
     
    Lewis, Nov 2, 2011
    #19
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