[DRBD-user] CLVM over DRBD speed test

Raoul Bhatia [IPAX] r.bhatia at ipax.at
Thu Jul 2 15:28:13 CEST 2009


hi,

Federico Simoncelli wrote:
> On Thu, Jul 2, 2009 at 10:39 AM, Florian Haas<florian.haas at linbit.com> wrote:
>> Federico,
>>
>> out of curiosity: does this throughput drop also occur when you activate
>> your "TestGroup00" VG in exclusive mode?
> 
> Hi Florian,
> I did the tests again using just LVM:
> 
> # pvcreate /dev/cciss/c0d0p1
> # vgcreate -cn TestGroup00 /dev/cciss/c0d0p1
> # lvcreate -n TestSpeed00 -L 4G TestGroup00
> # sync && dd if=/dev/zero of=/dev/TestGroup00/TestSpeed00 bs=1M
> count=100 oflag=direct
> 104857600 bytes (105 MB) copied, 1,45695 seconds, 72,0 MB/s
> # pvs
>   PV                VG          Fmt  Attr PSize   PFree
>   /dev/cciss/c0d0p1 TestGroup00 lvm2 a-   465,73G 461,73G
> 
> 
> # sync && dd if=/dev/zero of=/dev/drbd1 bs=1M count=100 oflag=direct
> 104857600 bytes (105 MB) copied, 1,7703 seconds, 59,2 MB/s
> 
> 
> # pvcreate /dev/drbd1
> # vgcreate -cn TestGroup00 /dev/drbd1
> # lvcreate -n TestSpeed00 -L 4G TestGroup00
> # sync && dd if=/dev/zero of=/dev/TestGroup00/TestSpeed00 bs=1M
> count=100 oflag=direct
> 104857600 bytes (105 MB) copied, 7,3782 seconds, 14,2 MB/s
> # pvs
>   PV         VG          Fmt  Attr PSize   PFree
>   /dev/drbd1 TestGroup00 lvm2 a-   465,71G 461,71G

just for the records, i do not think that testing disk-speed with a
~100MB file when your controller has 128MB cache is a good indicator.

moreover, the protocol in use might have a big impac there. quoting
from my commented drbd.conf

>   # C: write IO is reported as completed, if we know it has
>   #    reached _both_ local and remote DISK.
>   #    * for critical transactional data.

*maybe* this is the issue. drbd waits for an ack from the disk subsystem
requesting the controller to write the data to the disks whereas (c)lvm
is happy as soon as the data hits the controller cache.

of course, i might be wrong ;)

cheers,
raoul
-- 
____________________________________________________________________
DI (FH) Raoul Bhatia M.Sc.          email.          r.bhatia at ipax.at
Technischer Leiter

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Barawitzkagasse 10/2/2/11           email.            office at ipax.at
1190 Wien                           tel.               +43 1 3670030
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