[DRBD-user] CLVM over DRBD speed test

Federico Simoncelli federico.simoncelli at gmail.com
Thu Jul 2 16:00:43 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 Thu, Jul 2, 2009 at 3:49 PM, Florian Haas<florian.haas at linbit.com> wrote:
>>> Hi Florian,
>>> I did the tests again using just LVM:
> What do you mean, you changed back to locking_type = 1?

I was too lazy for that :-)
I stopped cman, and I used the option -cn with vgcreate. This should be enough.

>> 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).

I'm not testing the disk/controller speed as absolute value.
I don't want to make comparison with other disks/controllers, I'm
trying to measure the performances at each level: disk, drbd, lvm,
filesystem and in this kind of comparison the controller cache has no
influence (it doesn't change between tests).

PS. just for the record the cache is split 50% for writing and 50% for
reading; so in my test only 64MB of cache were involved.

>> *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.

...and I would also add that the test over drbd was quite good (I'm
sure it can be tuned to achieve even better performances):

# 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


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