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

[Rafael Micó Miranda]

Hi Michael

El mié, 03-03-2010 a las 11:16 -0800, Michael @ Professional Edge LLC
escribió:

> Hail Linux Cluster gurus,
> 


[...]


> 
>  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...
> 


You can find an unofficial MDADM rgmanager resource script at this
topic:

https://www.redhat.com/archives/linux-cluster/2009-August/msg00111.html

The resource was developed by Brem Belguebli, maybe if he sees this
topic he could give you more detail of the capabilities of the resource
script and it's compatibility with LVM / CLVM on top of it.

In the other hand, you can use directly mirrored LVM volumes with CLVM.
I made some testing with the behaviours of mirrored LVM and I found some
strange stuff when only one node fails its connection to the device - in
your situation it will happen when one of the nodes fails one of the
links with one of the shelves. The fact was the device being marked as
"unknown device" in the node with the failed path, and in the other
everything seemed ok. What can happen during the "reconstruction" of the
failed volume can be unpredictable. Note the "99.6" in the Copy% column,
it always had the same value while the path was failed:

NODE A
lvs -a -o +vg_name,device
LV                      VG       Attr   LSize   Origin Snap%  Move Log
Copy%  Convert VG
Devices                                          
logvolquorum            volgrp01 mwi-ao 996,00M
logvolquorum_mlog 100,00         volgrp01
logvolquorum_mimage_0(0),logvolquorum_mimage_1(0)
[logvolquorum_mimage_0] volgrp01 iwi-ao 996,00M
volgrp01 /dev/mpath/quorum01(0)                           
[logvolquorum_mimage_1] volgrp01 iwi-ao 996,00M
volgrp01 /dev/mpath/quorum02(0)                           
[logvolquorum_mlog]     volgrp01 lwi-ao   4,00M
volgrp01 /dev/mpath/logquorum01(0)     


NODE B (failed path)
lvs -a -o +vg_name,device
LV                      VG       Attr   LSize   Origin Snap%  Move Log
Copy%  Convert VG
Devices                                          
logvolquorum            volgrp01 mwi-ao 996,00M
logvolquorum_mlog  99,60         volgrp01
logvolquorum_mimage_0(0),logvolquorum_mimage_1(0)
[logvolquorum_mimage_0] volgrp01 Iwi-ao 996,00M
volgrp01 /dev/mpath/quorum01(0)                           
[logvolquorum_mimage_1] volgrp01 Iwi-ao 996,00M
volgrp01 unknown device(0)                                
[logvolquorum_mlog]     volgrp01 lwi-ao   4,00M
volgrp01 /dev/mpath/logquorum01(0)   


I hope this brings some light to your questions.

Cheers,

Rafael

-- 
Rafael Micó Miranda
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