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Re: [Linux-cluster] Home-brew SAN/iSCSI


On Sat, 10 Oct 2009 15:41:33 -0400, Madison Kelly 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.
> > 

In addition to IET and iSCSI client you may want to take a look at multipath
too. I am also testing a home-brew SAN setup with two storage machines and
replicated via DRBD GFS2 partition (Primary/Primary) which in turn is exported
from both via iSCSI and then imported on the nodes with multipath to both
storages - the idea is to have the performance from both and no single point
of failure for the storage too.

> > -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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