sparse files patch question

devzero at devzero at
Fri Aug 7 02:14:49 MDT 2009


i just came across the sparse-block patch. 

i`m using rsync to store vmware vmdk virtual disks to a zfs filesystem.
vmdk files have large portions of zeroed data and when thin provisioned (not being used yet), they even may be sparse.
on the target, after writing to zfs the zeroes are always efficiently stored/compressed, i.e. they take no additional space on zfs.

is this patch worth a try here to speed things up ?

i`m a little bit unsure, but i assume "no" as this is to be used when llseek() is costly, correct ?

i`m asking as i don`t want to waste time with experiments at a customer site.


This patch adds the --sparse-block option.  Andrea Righi writes:

  In some filesystems, typically optimized for large I/O throughputs (like
  IBM GPFS, IBM SAN FS, or distributed filesystems in general) a lot of
  lseek() operations can strongly impact on performances. In this cases it
  can be helpful to enlarge the block size used to handle sparse files
  directly from a command line parameter.

  For example, using a sparse write size of 32KB, I've been able to
  increase the transfer rate of an order of magnitude copying the output
  files of scientific applications from GPFS to GPFS or GPFS to SAN FS.


To use this patch, run these commands for a successful build:

    patch -p1 <patches/sparse-block.diff
    ./configure                               (optional if already run)
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