Re: [Nbd] Performance numbers?

[Wouter Verhelst <w@...112...>]

On Wed, Sep 17, 2008 at 04:08:43PM -0700, Edward Muller wrote:
> Does anyone have any performance numbers on nbd vs things like nfs,  
> san vendor offerings, etc?

Linux magazine did an article about netbooting diskless clients a few
years ago, and that has some comparative numbers between NFS, NBD, and a
bunch of other variants of NBD. I'm offline right now and don't have the
URL with me, but there's a link on <http://nbd.sf.net/>. Other than
that, I'm not aware of any performance comparisons; but my gut feeling
is that NBD is probably faster, since the protocol is so extremely
simple and low overhead.

> How about information on failover of an nbd 'server' from one machine  
> to another?

Why the quotes?

I'm not entirely sure on what you mean with failover. If you mean having
an NBD client connected to one machine automatically reconnecting to
another when its server goes down, then there currently is no support
for that. A while back there was talk about having the kernel module
block access to the block device until the client exits; I don't know
what happened to that, but if it got merged, then it should be
reasonably straightforward to implement failover as part of nbd-client.

Having said that, it is perfectly possible to create a failover cluster
with RAID-over-NBD and heartbeat. To do that, you'd run a software RAID1
over a local block device on the one hand and an NBD device on the
other; the other machine would run nbd-server, and you'd switch places
when heartbeat tells us that the machine running the RAID1 is dead.

-- 
<Lo-lan-do> Home is where you have to wash the dishes.
  -- #debian-devel, Freenode, 2004-09-22