6:10 p.m.
On Thu, Jan 12, 2017 at 6:01 PM, Nicolas Ecarnot <nicolas(a)ecarnot.net> wrote:
Hi,
As we are using a very similar hardware and usage as Mark (Dell poweredge
hosts, Dell Equallogic SAN, iSCSI, and tons of LUNs for all those VMs), I'm
jumping into this thread.
Can you share your multipath.conf that works with Dell Equallogic SAN?
Le 12/01/2017 à 16:29, Yaniv Kaul a écrit :
While it's a bit of a religious war on what is preferred with iSCSI -
network level bonding (LACP) or multipathing on the iSCSI level, I'm on the
multipathing side. The main reason is that you may end up easily using just
one of the paths in a bond - if your policy is not set correct on how to
distribute connections between the physical links (remember that each
connection sticks to a single physical link. So it really depends on the
hash policy and even then - not so sure). With iSCSI multipathing you have
more control - and it can also be determined by queue depth, etc.
(In your example, if you have SRC A -> DST 1 and SRC B -> DST 1 (as you seem
to have), both connections may end up on the same physical NIC.)
>
>
> If we reduce the number of storage domains, we reduce the number of
> devices and therefore the number of LVM Physical volumes that appear in
> Linux correct? At the moment each connection results in a Linux device which
> has its own queue. We have some guests with high IO loads on their device
> whilst others are low. All the storage domain / datastore sizing guides we
> found seem to imply it’s a trade-off between ease of management (i.e not
> having millions of domains to manage), IO contention between guests on a
> single large storage domain / datastore and possible wasted space on storage
> domains. If you have further information on recommendations, I am more than
> willing to change things as this problem is making our environment somewhat
> unusable at the moment. I have hosts that I can’t bring online and therefore
> reduced resiliency in clusters. They used to work just fine but the
> environment has grown over the last year and we also upgraded the Ovirt
> version from 3.6 to 4.x. We certainly had other problems, but host
> activation wasn’t one of them and it’s a problem that’s driving me mad.
I would say that each path has its own device (and therefore its own queue).
So I'd argue that you may want to have (for example) 4 paths to each LUN or
perhaps more (8?). For example, with 2 NICs, each connecting to two
controllers, each controller having 2 NICs (so no SPOF and nice number of
paths).
Here, one key point I'm trying (to no avail) to discuss for years with
Redhat people, and either I did not understood, either I wasn't clear
enough, or Redhat people answered me they owned no Equallogic SAN to test
it, is :
My (and maybe many others) Equallogic SAN has two controllers, but is
publishing only *ONE* virtual ip address.
On one of our other EMC SAN, publishing *TWO* ip addresses, which can be
published in two different subnets, I fully understand the benefits and
working of multipathing (and even in the same subnet, our oVirt setup is
happily using multipath).
But on one of our oVirt setup using the Equallogic SAN, we have no choice
but point our hosts iSCSI interfaces to one single SAN ip, so no multipath
here.
At this point, we saw no other mean than using bonding mode 1 to reach our
SAN, which is terrible for storage experts.
To come back to Mark's story, we are still using 3.6.5 DCs and planning to
upgrade.
Reading all this is making me delay this step.
--
Nicolas ECARNOT
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