[Linux-cluster] iSCSI GFS

[Gordan Bobic]

isplist at logicore.net wrote:
> My thread on SSI/VM/Sharedroot got me thinking because of the input some of 
> you have put into the thread. There is some very valuable information in 
> there. 
> 
> In fact, it got me wondering if my FC path might not be the greatest based on 
> Gordan's (I think it was) input on the subject. I've also seen a few posts 
> about iSCSI lately. Can anyone shed a little light on iSCSI and what I would 
> need to give it a try.

iSCSI is just a connection protocol like Fibre Channel. They both do the 
same thing. iSCSI works over ethernet, while FC works over fibre. iSCSI 
is cheaper, and FC has traditionally been faster (although the point 
gets a bit moot with 1Gb and 10Gb ethernet as the storage stops being 
the bottleneck.

> Can iSCSI be used to run a clustered LAMP setup which would be as flexible as 
> FC for growth and management?

iSCSI and FC are equivalent. I personally prefer iSCSI because it's 
cheaper. In terms of features there isn't a great deal to choose between 
them.

> Preferably, without having to buy any hardware to try it out :). I've already 
> got FC gear but it looks like iSCSI is much easier to deal with. I read 
> somewhere or had found, an open source iSCSI target driver no less. 

Yes, iSCSI is now ISS pretty much end-to-end. But if you already have FC 
gear and if you have the required drivers for it, then there's no need 
to replace it.

Here is another thing you may find interesting:
http://sourceware.org/cluster/ddraid/
I stumbled upon it last night, and the ides seems great - network RAID 
3.5 (n+1 like RAID 3,4,5). It seems to make sense for small-ish 
clusters, or situations where you are stacking RAID / cluster levels 
(e.g. RAID 3.5+3.5). But without the ability to dynamically add drives 
(like in standard MD software RAID) I'm not sure how useful it would be 
if you need a scaleable solution. It also wouldn't allow you to power 
down half of your cluster at off-peak times.

Gordan