[Lustre-discuss] Lustre and iSCSI

[Cliff White]

David Pratt wrote:
> Hi. I am exploring possibilities for pooled storage for virtual 
> machines. Lustre looks quite interesting for both tolerance and speed. I 
> have a couple of basic questions:
> 
> 1) Can Lustre present an iSCSI target

Lustre doesn't present target, we use targets, and we should work fine 
with iSCSI. We don't have a lot of iSCSI users, due to performance 
concerns.

> 2) I am looking at physical machines with 4 1TB 24x7 drives in each. How 
> many machines will I need to cluster to create a solution with provide a 
> good level of speed and fault tolerance.
> 
'It depends' - what is a 'good level of speed' for your app?

Lustre IO scales as you add servers. Basically, if the IO is big enough, 
the client 'sees' the bandwidth of multiple servers.  So, if you know 
the  bandwidth of 1 server (sgp_dd or other raw IO tools helps) then 
your total bandwidth is going to be that figure, times the number of 
servers. This assumes whatever network you have is capable of sinking 
this bandwidth.

So, if you know the IO you need, and you know the IO one server can 
drive, you just divide the one by the other.

Fault tolerance at the disk level == RAID.
Fault tolerance at the server level is done with shared storage 
failover, using linux-ha or other packages.
hope this helps,
cliffw

> Many thanks.
> 
> Regards,
> David
> 
> 
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