[DRBD-user] CLVM over DRBD speed test

Florian Haas florian.haas at linbit.com
Thu Jul 2 15:49:02 CEST 2009

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On 2009-07-02 15:28, Raoul Bhatia [IPAX] wrote:
> 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:

What do you mean, you changed back to locking_type = 1?

> 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.

Nonetheless 50 MB/s write speed per disk is a reasonable expectation on
current hardware, and 14.2 MB/s would be way too slow. Still, it's
probably wise to rerun the test writing one big chunk that fits into
memory (RAM), but not into the on-controller cache. Something like bs=1G
count=1 (assuming you have more than 2G or so RAM).

> 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 ;)

You are, because the original intention was to use DRBD together with
CLVM, which requires running DRBD in dual-Primary mode, which in turn
necessitates protocol C.


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