[Linux-cluster] Home-brew SAN/iSCSI

[Corey Kovacs]

One thing to keep in mind is the fact that iscsi is a tcp based protocol. So
even though your machine might be doing nothing but acting as an iscsi
target, it's going to take the brunt of the load in handling the tcp stack.
If you can get a network card that handles iscsi on the card itself, that
will help loads. Otherwise your cpu might dig a hole for itself to crawl
into.

Of course if your just messing about, or only using the iscsi targets
locally, then your probably ok.

Benefits of a dedicated device are management capabilities, throughput,
flexible location, etc. Fibre channel is 8Gb standard now and SAN's are
starting to use it instead of 4Gb, but the entry point in terms of cost is
high. A fully loaded EVA8100 can cost 250k, the FC infrastructure can go to
60-80k easily. iscsi really needs to have a seperate back end storage
network to be useful and it should be 10Gb. I hear people say it's useful on
slower hardware but everyone has an opinion. I guess if your just using it
for system volumes and low IO then 1G might be fine.

Anyway hope this help and if it doesnt' at least it might give you more to
think about.


Best of luck

Corey


On Sat, Oct 10, 2009 at 8:41 PM, Madison Kelly <linux at alteeve.com> wrote:

> Andrew A. Neuschwander wrote:
>
>> Madison Kelly wrote:
>>
>>> Hi all,
>>>
>>>  Until now, I've been building 2-node clusters using DRBD+LVM for the
>>> shared storage. I've been teaching myself clustering, so I don't have a
>>> world of capital to sink into hardware at the moment. I would like to start
>>> getting some experience with 3+ nodes using a central SAN disk.
>>>
>>>  So I've been pricing out the minimal hardware for a four-node cluster
>>> and have something to start with. My current hiccup though is the SAN side.
>>> I've searched around, but have not been able to get a clear answer.
>>>
>>>  Is it possible to build a host machine (CentOS/Debian) to have a simple
>>> MD device and make it available to the cluster nodes as an iSCSI/SAN device?
>>> Being a learning exercise, I am not too worried about speed or redundancy
>>> (beyond testing failure types and recovery).
>>>
>>> Thanks for any insight, advice, pointers!
>>>
>>> Madi
>>>
>>>
>> If you want to use a Linux host as a iscsi 'server' (a target in iscsi
>> terminiology), you can use IET, the iSCSI Enterprise Target:
>> http://iscsitarget.sourceforge.net/. I've used it and it works well, but
>>  it is a little CPU hungry. Obviously, you don't get the benefits of a
>> hardware SAN, but you don't get the cost either.
>>
>> -Andrew
>>
>
> Thanks, Andrew! I'll go look at that now.
>
>  I was planning on building my SAN server on an core2duo-based system with
> 2GB of RAM. I figured that the server will do nothing but host/handle the
> SAN/iSCSI stuff, so the CPU consumption should be fine. Is there a way to
> quantify the "CPU/Memory hungry"-ness of running a SAN box? Ie: what does a
> given read/write/etc call "cost"?
>
>  As an aside, beyond hot-swap/bandwidth/quality, what generally is the
> "advantage" of dedicated SAN/iSCSI hardware vs. white box roll-your-own?
>
> Thanks again!
>
> Madi
>
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