re[2]: drbd on 2.4 or sth else?

[sean.upton@uniontrib.com]

So I guess the easy answer is use a DAS RAID device with multiple RAID
controllers (Active/Passive config, with failover) in the device enclosur=
e,
but don't bother worrying about having more than one SCSI controller in e=
ach
server host; if the SCSI adapter fails, the whole host does, but that's o=
kay
since you have another node to take over (via heartbeat)...

Sean

-----Original Message-----
From: Ragnar Kj=F8rstad [mailto:linux-ha@ragnark.vestdata.no]
Sent: Friday, August 31, 2001 1:23 PM
To: Greg Freemyer
Cc: Omer Faruk Sen; linux-ha@muc.de
Subject: Re: re[2]: drbd on 2.4 or sth else?


On Tue, Aug 28, 2001 at 11:39:08AM -0400, Greg Freemyer wrote:
> At this time GFS does not support "software" mirroring.  In addition, I
think=20
> GFS only supports Fibre-Channel, so it is not a cheap thing to get into.
(In=20
> theory GFS supports SCSI, but it uses a new feature/technology that was
not=20
> available in shipping drives a couple of months ago.  That may have
changed.)

As far as I know GFS works fine with SCSI.

You can put two scsi controllers on the same bus, but that's not good
for either performance or availability. The best solution is to use a
RAID-controller with multiple scsi buses. This doesn't scale to a large
number of nodes though - if you need that FC is the way to go.

> There is an entire range of these external raid controllers/chassis wit=
h
prices=20
> ranging from a few thousand to a few million (an EMC Symmetrix starts a=
t
one=20
> million dollars).
>=20
> If you truly want a HA RA you need to get one with dual interfaces and
internal=20
> duplication. One issue here is GFS support of "Multi-pathing".  I don't
know if=20
> GFS supports this yet or not.  Many serious O/S's designed to connect t=
o a
SAN=20
> do.

No, multipathing is not really an issue. If you e.g. use a
RAID-controller with two host interfaces and connected to two different
hosts each host only have one path to the storage.

There are also patches for linux to support real multipath (for failover=20
or multipath), but if you're using gfs you can provide high availability
and high performance by using multiple nodes - so you don't need
multiple paths from each host.



--=20
Ragnar Kjorstad
Big Storage

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