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

[Jim Klimov]

On 2012-11-16 13:12, Brian Hechinger wrote:
> On Nov 16, 2012, at 9:35, Florian <florian at acw.at> wrote:
>
>> Hi,
>>
>> The Problem with the BladeCenter is, that there are only two network ports an all blades, for two switches. It is possible put put two more switches in it, but have to buy than extra network cards for all blades.
>>
>> Maybe, I can talk to my CEO to buy one or two more switches and networkcards, but before that, I have to submit some good statements, if a raid over two iSCSI targets is possible and works well.
>
> 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.

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.

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).

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).

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

My 2c,
//Jim