Re: [Xen-users] Differences in performance between file and LVM based images

[Christoph Purrucker <cp+ml-xen@xxxxxxxx>]

Hi Alex,

> Having said that, I invite you (everybody, not just you) to continue
> with these kind of benchmarks. If you test the actual overhead of each
> system and manage to eliminate all the caching, I'd be interested in
> seeing your results.
 :)  I knew I was going to get that. *g*

Hardware: Athlon XP 1600+, 512 MB RAM, one single and old ATA-Disk
Software: Debian Etch, 2.6.16-2-xen-k7 both on Dom0 and 2.6.16-2-k7 on
DomU (Debian-Standard-Kernels out of the box)

Dom0 Memory: 256MB total, 5MB free, 60MB cache
DomU Memory: 64MB total, 25MB free + 25MB cache (it's a clean image)


==== Dom0 speed on physical harddisk ====

Dom0# iozone -KoMe -s900m -r256k -i0 -i1 -i2 -f /var/tmp/iotest

                                                   random  random
    KB  reclen   write rewrite    read    reread    read   write
921600     256   11854   18220    23382    25178   10965   11992


==== DomU speed on loopback file ====

DomU# iozone -KoMe -s900m -r256k -i0 -i1 -i2 -f /var/tmp/iotest

                                                  random  random
    KB  reclen   write rewrite    read    reread    read   write
921600     256   11478   14609    15998    18539    7280   14882

The test costed 52 CPU seconds on Dom0 and 42 CPU seconds on DomU 
(according to xentop).

==== DomU speed on LVM volume ====

DomU# iozone -KoMe -s900m -r256k -i0 -i1 -i2 -f /mnt/tmp/iotest

                                                  random  random
    KB  reclen   write rewrite    read    reread    read   write
921600     256   10382   15908    18942    18639    7267    8815


This test costed 16 CPU seconds on Dom0 and 39 CPU seconds on DomU 
(according to xentop).
Please note that the LVM PV is at the slow end of the harddisk, the 
loopback file is somewhere in the first half of the disk. I made the 
last two tests twice with no striking differences.
What's the conclusion now?

- More tests needed!
- I think 16 seconds to 52 seconds on Dom0 is a remarkable difference.

cu cp

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