Re: Extreme CPU usage by enbd-client?

Peter T. Breuer wrote:


>>Didn't show anything at all. What block size would you advise on a
>>GBit-network?
> 
> 
> It doesn't matter, if requests are aggregated anyway!
True.


>>Maybe I'm making a terrible mistake here, but I've got four different
>>machines acting as a "storage server", each exporting one block device.
>>There's one "frontend" machine which connects to the four servers and
>>imports the block devices. Per block device (= per server), two channels
>>are used (default). So why are you surprised about the amount of
>>clients? Am I doing something fundamentally wrong?
> 
> 
> Well, if you were making a raid5 with an enbd device the idea would be
> to have one local resource and two remote ones (on each of three
> machines) so that if one machine dies the other two machines can carry
> on using their local resource and one imported remote resource in each
> raid5 array.
> 
> That's two clients per machine.
OK, I understand what you're saying here, but the idea I had was to
create a "cluster" of old machines (each containing a bunch of harddrive
space). In the configuration you're suggesting, every machine needs to
be quite modern and fast, correct me if I'm wrong.
However, the setup I had in mind:

              ISS01  ISS02  ISS03  ISS04   FRONTEND
(200GB each)  hda5   hda5   hda5   hda5    md0 (nda,ndb,ndc,ndd)
(300GB each)  hdb1   hdb1   hdb1   hdb1    md1 (nde,ndf,ndg,ndh)

("iss" = "infinity storage server", the name I gave the setup)

In this setup, the frontend runs two RAID5 arrays (md0, md1) which are
combined in one large LVM volume of (200GB * 3+300GB * 3 =) 1500 GB. As
far as I can see, this kind of setup is not possible when using clients
and servers combined on all machines.
By the way: it's perfectly possible to create a secundary frontend to
avoid the primary frontend becoming a "single point of failure".
As you can see, my objectives are:
1) large amount of diskspace
2) reliability should be offered (limited, though. RAID5 is enough)
3) diskspace should be extensible

Of course: any suggestions/bright idea's/flames on this setup are very,
very welcome!

--Bas