[OpenIndiana-discuss] Linux software-raid with two Comstar iSCSI volumes

[Brian Hechinger]

On Nov 16, 2012, at 11:33, Jim Klimov <jimklimov at cos.ru> wrote:

> On 2012-11-16 13:12, Brian Hechinger wrote:
>> 
>> 
>> Have you considered vlan trunking?
> 
> As he said, they have an external and an internal network segment.
> It might be an architectural or even a political/compliance requirement
> to keep the two network segments physically separate.

Or it may not. We won't know without asking though. :)

> Well, in this case they have a segment for storage traffic, which may
> be assumed to be saturated with bulky IOs, and that would compromise
> performance for "application data" traffic if done by the same switch
> hardware. Then again, if the said applications would lag because of
> slow virtual disk components - there may be reason in trunking both
> networks and separating data by VLANs.

You aren't magically increasing the usage of the switches if you implement trunking, however. You'd be splitting each network's load across both. With some care the result should be close to net zero on the load front possibly giving more bandwidth to SAN where it is more than likely needed anyway.

> However, in general two separate switches allow you to do failover or
> IPMP, not LACP (there are some models that allow LACP over several
> interconnected switches, which seem like one switch to the connected
> server or another device for the purpose of link aggregation; Nortel
> had this for a while, and Cisco may have it in recent models).

Yes, the Nexus switches do that with their Virtual Port Channel stuff.

> But if some means of roundrobining over two separate subnets on two
> switches is an option for the storage and higher-level apps - this may
> be quite a reasonable option to boost reliability and possibly level
> out the performance (switch saturation).

He said iSCSI therefor he should be able to do MPIO with a round robin policy to achieve this. I believe Linux can do this.

> The possible performance implications (half-gbE for writes, GbE for
> reads) were addressed by other posters :)

Yes, I won't be touching that. :)

> My 2c,

There, I've added my half a cent's worth. :)

-brian