[Linux-cluster] Storage Cluster Newbie Questions - any help with answers greatly appreciated!

[Leo Pleiman]

One solution would be to build the two machines as a two node cluster. Qdisk is normally recommended but two node clusters are supported without it. Use the cluster resource manager to control md management of the FCAL drives. You'll need to disable md startup and create a custom script to allow the cluster resource manager to start and stop the md devices. I would build three cluster resources; md disk, nfs, and samba making nfs and samba dependent on md disk. You'll need a failover domain consisting of both machines. When you're done you'll have on machine doing nothing but waiting for the services on the other machine to fail over. Personally, I would build each FCAL shelf as a RAID5 or RAID6 array, presenting md0 and md1 to LVM. I wouldn't use RAID1 unless you have very little confidence in your hardware. GFS can't be used with software raid and since you won't be using GFS you won't need a fence device.

Leo J Pleiman 
Senior Consultant 
Red Hat Consulting Services 
410.688.3873

"Red Hat Ranked as #1 Software Vendor for Fifth Time in CIO Insight Study"

----- Original Message -----
From: "Michael @ Professional Edge LLC" <m3 at professionaledgellc.com>
To: linux-cluster at redhat.com
Sent: Wednesday, March 3, 2010 2:16:07 PM GMT -05:00 US/Canada Eastern
Subject: [Linux-cluster] Storage Cluster Newbie Questions - any help with answers greatly appreciated!

Hail Linux Cluster gurus,

I have researched myself into a corner and am looking for advice.  I've 
never been a "clustered storage guy", so I apologize for the potentially 
naive set of questions.  ( I am savvy on most other aspects of networks, 
hardware, OS's etc... but not storage systems).

I've been handed ( 2 ) x86-64 boxes w/2 local disks each; and ( 2 ) 
FC-AL disk shelves w/14 disks each; and told to make a mini NAS/SAN (NFS 
required, GFS optional).  If I can get this working reliably then there 
appear to be about another ( 10 ) FC-AL shelves and a couple of Fiber 
Switches laying around that will be handed to me.

NFS filesystems will be mounted by several (less than 6) linux machines, 
and a few (less than 4) windows machines [[ microsoft nfs client ]] - 
all more or less doing web server type activities (so lots of reads from 
a shared filesystem - log files not on NFS so no issue with high IO 
writes).  I'm locked into NFS v3 for various reasons.  Optionally the 
linux machines can be clustered and GFS'd instead - but I would still 
need to come up with a solution for the windows machines - so a NAS 
solution is still required even if I do GFS to the linux boxes.

Active / Passive on the NFS is fine.

* Each of the ( 2 ) x86-64 machines have a Qlogic dual HBA 1 fiber 
direct connected to each shelf  (no fiber switches yet - but will have 
them later if I can make this all work); I've loaded RHEL 5.4 x86-64.

* Each of the ( 2 ) RHEL 5.4 boxes - used the 2 local disks w/onboard 
fake raid1 = /dev/sda - basic install so /boot and LVM for the rest - 
nothing special here (didn't do mdadm basically for simplicity of /dev/sda)

* Each of the ( 2 ) RHEL 5.4 boxes can see all the disks on both shelves 
- and since I don't have Fiber Switches yet - at the moment there is 
only 1 path to each disk; however as I assume I will figure out a method 
to make this work - I have enabled multipath - and therefore I have 
consistent names to 28 disks.

Here's my dilemma.  How do I best add Redundancy to the Disks, removing 
as many single points of failure, and preserving as much diskspace as 
possible?

My initial thought was - to take "shelf1:disk1 and shelf2:disk1" and put 
them into a software raid1 - mdadm; then put the resulting /dev/md0 into 
a LVM.  When I need more diskspace, I just then create "shelf1:disk2 and 
shelf2:disk2" as another software raid1 then just add the new "/dev/md1" 
into the LVM and expand the FS. This handles a couple things in my mind:

1. Each shelf is really a FC-AL so it's possible that a single disk 
going nuts could flood the FC-AL and all the disks in that shelf go poof 
until the controller can figure itself out and/or the bad disk is removed.

2. Efficient I am retaining 50% storage capacity after redundancy - if I 
can do the "shelf1:disk1 + shelf2:disk2" mirrors; plus all bandwidth 
used is spread across the 2 HBA fibers and nothing goes over the TCP 
network.  Conversely DRBD doesn't excite me much - as I then have to do 
both raid in the shelf (probably still with MDADM) and then I add TCP 
(ethernet) based RAID1 between the nodes - and when all is said and done 
- I only the have 25% of storage capacity still available after redundancy.

3. I easy to add more diskspace - as each new mirror (software raid1) 
can just be added to an existing LVM.

 From what I can find messing with Luci (Conga) though... is - I don't 
see any resource scripts listed for - "mdadm" (on RHEL 5.4) - so would 
my idea even work  (I have found some posts asking for a mdadm resource 
script but I've seen no response)?  I also see with RHEL 5.3 LVM has 
mirrors that can be clustered now - is this the right answer?  I've done 
a ton of reading but everything I've dug up so far; assumes that the 
fiber devices are being presented by a SAN that is doing the redundancy 
before the RHEL box sees the disk... or... there are a ton of examples 
of where fiber is not in the picture and there are a bunch of locally 
attached hosts presenting storage onto the TCP (ethernet) - but I've not 
found nearly anything on my situation...

So... here I am... :-)  I really just have 2 nodes - who can both see - 
a bunch of disks (JBOD) and I want to present them to multiple hosts via 
NFS (required) or GFS (to linux boxes only).

All ideas - are greatly appreciated!

-Michael

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