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

[Kaloyan Kovachev]

Hi,

On Wed, 03 Mar 2010 11:16:07 -0800, Michael @ Professional Edge LLC wrote
> 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.

Why not start NFS/Samba on both machines with only the IP floating between
them then?

> 
> * 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.
> 

You may create RAID1 (between the two shelfs) over RAID6 (on the disks from
the same shelf), so you will loose only 2 more disks per shelf or about 40%
storage space left, but more stable and faster. Or several RAID6 arrays with
2+2 disks from each shelf - again 50% storage space, but better performance
with the same chance for data loss like with several RAID1 ... the resulting
mdX you may add to LVM and use the logical volumes

>  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).
> 

if the Windows and Linux data are different volumes it is better to leave the
GFS partition(s) available only via iSCSI to the linux nodes participating in
the cluster and not to mount it/them locally for the NFS/Samba shares, but if
the data should be the same you may go even Active/Active with GFS over iSCSI
[over CLVM and/or] [over DRBD] over RAID and use NFS/Samba over GFS as a
service in the cluster. It all depends on how the data will be used from the
storage

> All ideas - are greatly appreciated!
> 
> -Michael
> 
> --
> Linux-cluster mailing list
> Linux-cluster at redhat.com
> https://www.redhat.com/mailman/listinfo/linux-cluster