On Wed, Sep 09, 2009 at 09:41:05PM +0200, Robert wrote:
> Hi,
>
> I'm investigating slow file transfer speeds between two SATA disks
> connected to an Intel ICH10R (ahci).
> Some files copy at a good speed of about ~80MB/s other are as slow as
> only ~4MB/s.
> I suspect that those files might be heavily fragmented and the transfer
> suffers from bad random read performance.
>
> How can I check which blocks a file occupies?
> Is there some tool i am missing to get the info from the inode?
I really wouldn't know, but typically ffs isn't really susceptible to
fragmentation unless it's almost completely full (and the default
settings leave at least 5% of disk space for root; you'll also see
"switching from TIME to SPACE" or something similar in the dmesg,
indicating that the filesystem is nearly full and will now try to
conserve space instead of speeding aceess, which does mean it'll
fragment badly.)
What happens when you create a new file, say using dd, and try to read
that back? Is your file system nearly full? Did you use sufficiently
large files to even out the effects of read and write caches, either on
disk or in the OS? Can you post a dmesg and the results of dd on
seemingly-similar files? Have you confirmed that it indeed depends on
the file and not something else (i.e. are "fast" files always fast, and
"slow" files always slow)?
Joachim
