On Thu, May 03, 2007 at 02:15:45PM -0700, Bakul Shah wrote: > [originally reported for ZFS on FreeBSD but Pawel Jakub Dawid > says this problem also exists on Solaris hence this email.]
Thanks!
> Summary: on ZFS, overhead for reading a hole seems far worse
> than actual reading from a disk. Small buffers are used to
> make this overhead more visible.
>
> I ran the following script on both ZFS and UF2 filesystems.
>
> [Note that on FreeBSD cat uses a 4k buffer and md5 uses a 1k
> buffer. On Solaris you can replace them with dd with
> respective buffer sizes for this test and you should see
> similar results.]
>
> $ dd </dev/zero bs=1m count=10240 >SPACY# 10G zero bytes allocated
> $ truncate -s 10G HOLEY # no space allocated
>
> $ time dd <SPACY >/dev/null bs=1m # A1
> $ time dd <HOLEY >/dev/null bs=1m # A2
> $ time cat SPACY >/dev/null # B1
> $ time cat HOLEY >/dev/null # B2
> $ time md5 SPACY # C1
> $ time md5 HOLEY # C2
>
> I have summarized the results below.
>
> ZFS UFS2
> Elapsed System Elapsed System Test
> dd SPACY bs=1m 110.26 22.52 340.38 19.11 A1
> dd HOLEY bs=1m 22.44 22.41 24.24 24.13 A2
>
> cat SPACY 119.64 33.04 342.77 17.30 B1
> cat HOLEY 222.85 222.08 22.91 22.41 B2
>
> md5 SPACY 210.01 77.46 337.51 25.54 C1
> md5 HOLEY 856.39 801.21 82.11 28.31 C2
This is what I see on Solaris (hole is 4GB):
# /usr/bin/time dd if=/ufs/hole of=/dev/null bs=128k
real 23.7
# /usr/bin/time dd if=/zfs/hole of=/dev/null bs=128k
real 21.2
# /usr/bin/time dd if=/ufs/hole of=/dev/null bs=4k
real 31.4
# /usr/bin/time dd if=/zfs/hole of=/dev/null bs=4k
real 7:32.2
--
Pawel Jakub Dawidek http://www.wheel.pl
[EMAIL PROTECTED] http://www.FreeBSD.org
FreeBSD committer Am I Evil? Yes, I Am!
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