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.
-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
I think what makes being an iSCSI target CPU hungry is that it is
handling a block layer protocol in user space. So while what it does is
fairly simple (i.e. no filesystem), it has to do a lot of it. Storage
performance is usually discussed in IOPS (I/Os Per Second), but when
rolling my own, I just throw enough spindles/raid/cpu/memory at it
saturate a GigE link and call it a day.
I've not used a hardware iSCSI SAN, just FC. The biggest benefits, in my
mind, of something like an EMC Clariion are the fully redundant hardware
path and the fast fabric.
Hmm, I may be getting off-topic here. Sorry about that.
-Andrew
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