[Stgt-devel] read << write

Robin Humble robin.humble+stgt
Thu Dec 6 09:40:54 CET 2007

On Thu, Dec 06, 2007 at 07:54:53AM +0900, FUJITA Tomonori wrote:
>On Wed, 5 Dec 2007 08:56:09 -0500 Robin Humble <robin.humble+stgt at anu.edu.au> wrote:
>> I'm finding that reads are a lot slower than writes when I have a real
>> file or device behind tgt instead of a ramdisk. is this expected?
>> iSER reads backed by a file on lustre or a md raid0 device seem to be at
>> most ~100MB/s which is 4 or 5 times slower than writes:
>Can you try a block-level benchmark like disktest to avoid file
>systems effects?

I'm afraid I don't have enough experience with disktest to know when
it's lying to me and/or when I'm driving it foolishly.

how about just large dd's?

                          write    read (MB/s)
 iSER + /dev/md0           333     110
 iSER + file on lustre     552     207
 iSER + ramdisk            905     410

 local /dev/md0            313     330
 local file on lustre      705     473
 local ramdisk            1600    2900

which are eg.
  dd if=/dev/zero of=/dev/sdc bs=1M count=10000
where 10G is >> (512M ram on initiator + 512M ram on target) so
buffering should be small.


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