[ENBD] RAID1 performance

[Ulrich Hahn]

On Mon, 27 Jan 2003, Peter T. Breuer wrote:

> "A month of sundays ago Ulrich Hahn wrote:"
> > The last few days I did some tests with the new RAID1 code.
>
> OK - thanks. That's 2.4.31, I take it.
>

I did not mention it, but you guessed right.

> > "make test" was flawless, but changing to 2 servers exporting
> > 100 GB each revealed some problems.
>
> OK. This is 1000 times bigger than any test I've done!

as I recall now, there is a minor Makefile "bug", not to be seen on a
single system setup. Client modules (enbd_bufferwr.o, enbd_ioctl.o) are
not copied to the client machine (make test).

>
> some details deleted
>
> > With a single nbd device it took 1:40 to dd 2 GB of data, that's
> > 20 MB/s. Using the RAID1 setup the same transfer took 8:30, that's
> > 4 MB/s. Monitoring traffic on the NIC the single device showed
> > oszillations between 15 and 30 MB/s, while the NICs in RAID setup
> > oszillated between 0 MB/s and 12 MB/s.
> >
> > Any comments on that?
>
> Let me think about it. In principle writes should be twice as slow (the
> way things are at the moment) with a single NIC if the NIC is the
> limiter, because twice the traffic goes across for the same result.
> Being twice as slow as that again is not in itself a disaster. I'd be
> pretty happy with that performace ... particularly as I decided to take
> the raid code out of the enbd device itself and put it in a separate
> driver, and am working on that at the moment.
>
> I'm very interested in that data. I'll ask you some questions later,
> when I get out of class.
>
> Petre

I also expected a factor of 2 on writes, but do not think the GbE-NICs
give a limit here.

Waiting for questions. Testing the fr module is also on my list.

Uli

: Dr. Ulrich Hahn             email: ulrich.hahn@zdv.uni-tuebingen.de :
: Zentrum f=FCr Datenverarbeitung            Tel: + (49) 07071 29 70315 :
: Universit=E4t T=FCbingen                     FAX: + (49) 07071 29  5912 :
-----------------------------------------------------------------------