[Linux-HA] Hardware requirements

[Helmut Wollmersdorfer]

igil at europesip.com wrote:

> I want to set up an HA linux cluster using the heardbeat software.
> Before to proceed, I was looking for the heardbeat cluster hardware 
> requirements.

Nothing special.
Which hardware you should add depends on which level of "high" 
availability you want.
The main idea behind HA is to have as many components as possible 
redundant to avoid SPOF http://wiki.linux-ha.org/SPOF.
The most important redundancy is related to heartbeat itself. It is 
recommended to have the communication link between the two nodes 
redundant. Different technologies should be preferred - e.g. serial/COM 
for one, and ethernet for the other. USBtoSerial will also work, and any 
technology which supports IP - e.g. IP over USB, IP over Firewire, WLAN. 
But with real serial and conventional ethernet you be on the easier and 
better tested side.

To use STONITH http://wiki.linux-ha.org/STONITH is also recommended. 
Linux-HA supports some STONITH devices like meatware (= human operator), 
software and hardware devices. Maybe you want to make your cluster 
perfekt after some time of testing, and you want to add a hardware 
STONITH device. To support this you need an appropriate interface - 
serial in most cases.

As you can see, having two serial interfaces would not be wrong.
BTW: My cluster has 15 cables on each node - interfaces are important.

> I need to know if I need an external SCSI disks or it could be internal to 
> the nodes. 
> For example, two nodes each node with one or more SCSI disk, sharing data 
> between them.
> If this second way to configure runs, could be this disks IDE disks?

This topic is related to the data resources needed by the services.
If the services need to have the same (or nearly the same) data on both 
nodes, the possibilities are:
1) shared storage devices (NAS, SAN etc.)
2) data replication (rsync, DRBD etc.)

DRBD http://www.drbd.org/ works with any block device as storage - 
harddisks (IDE, SCSI etc.), RAID, LVM. You can even use USB sticks, 
maybe CD/DVD-RW, or Flash. And it needs an IP connection to the other 
node, again you can use anything.

IMHO the main advantage of DRBD is the scalability beginning at very low 
cost.

This is my SOHO (Small Office Home Office) cluster:
- conventional PCs
- IDE/PATA/UDMA harddisks
- 2 NICs per node
- 1 NIC to LAN
- 1 NIC dedicated to DRBD
- 1 serial dedicated to heartbeat
- 1 self soldered RCD-serial STONITH device

Helmut Wollmersdorfer