[SATLUG] Create High Availability SAN from scratch

jaret jaret at aberlorn.com
Mon Jun 14 15:04:33 CDT 2010

Hi all. I'm a programmer trying to learn the costs of creating a 
high-availability SAN from scratch or buying from vendors (e.g. HP, 
QLogic, etc)  I've run into some questions that google hasn't helped out 
with, which makes me think I'm approaching this wrong.

First off, I have two servers (calling them HA-1) in a heartbeat 
configuration with DRBD running to keep data in sync. That way in case 
one server fails, the second server kicks in and all is good. This is 
high availability. Each computer has 8 1T hot-swappable drives with Raid 
1 applied. So, there's 8T total but with Raid 1, the server has 4T 
available to use. Question: is Raid 1 needed since I have DRBD running?  
(reference: http://www.drbd.org/home/mirroring/)

On the HA-1 servers, I make these iSCSI targets. Then from a client 
computer (the iSCSI initiator), I create the appropriate file systems on 
HA-1 and create a LVM logical volume.

Now, my storage needs increase and HA-1 is nearing capacity. I would 
then take two new servers and create HA-2, in the same manner I did with 
HA-1 previously. On the client computer, I would create appropriate file 
systems on HA-2 and then expand the existing LVM to include HA-2. In 
this way, the client sees the target as one physical volume, which would 
be 8T of usable drive space. Is this the right job for LVM or should I 
be using different software?

The current setup has a network transfer rate is 1000Mbps. If I wanted 
to increase this speed, I would put fibre network adapters using 
pci-express in the servers and hook them up to a fibre switch. Or I 
could do point-to-point to save cash but would probably be more 
difficult to administer. Any recommendations on going the fibre route? 
(good-bad experience with vendors/hardware?)



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