[CentOS] using CentOS as an iSCSI server?

Rudi Ahlers rudiahlers at gmail.com
Wed Oct 21 09:38:21 UTC 2009

On Wed, Oct 21, 2009 at 10:36 AM, Rainer Duffner <rainer at ultra-secure.de> wrote:
> Rudi Ahlers schrieb
>> John, you're right. iSCSI isn't an SMB replacement as I have learned
>> through all of this. SMB is good for sharing data between many PC's,
>> and even servers, but from what I understand it's also slower that
>> iSCSI and won't allow me to scale the storage by simply adding another
>> cheap server to the network. With iSCSI I could / should be able todo
>> that.
> iSCSI is just a protocol.
> It doesn't say anything about the underlying storage.
> http://en.wikipedia.org/wiki/ISCSI
> You can have a SAN (HP EVA, EMC, whatever) and still have that served
> via iSCSI by an additional piece of hardware you buy.
> Or you can have a NAS like NetApp and buy another of those ridiculously
> expensive licenses and then you can server iSCSI with that, too.
> What your storage looks like doesn't matter. The initiators just talk
> the iSCSI-protocol to the target.
>> OR am I approaching this from a different angle? If I wanted to setup
>> a server to serve content (in this case file storage, www, email &
>> SQL) to a network of computers, would iSCSI have served the purpose?
> Yes.
> Allthough, as iSCSI uses the ethernet-network, you need good switches.
> Because, your actually data-traffic has to go through the same network.
>> Or should I have kept using SMB? I am looking for a way to quickly
>> expand the whole setup though. If we need more space, then I just want
>> to add another cheap server with a 1TB HDD, and have it available on
>> the network. It is my impression that I could use iSCSI, probably
>> together with XFS, to accomplish this?
> No, it doesn't quite work like that.
> At least, for any trivial setup that doesn't involve some
> storage-virtualization software.
> If you can afford it, NetApp is a good solution for what you want to
> achieve.
> Or try one of the new SUN storage boxes.
> If that is out of your (financial) league, you can build the same
> functionality as the SUN OpenStorage boxes with your own hardware and
> OpenSolaris - although you will not have the extensive analytics and the
> ease of use of the GUI.
> I wouldn't use any of the cheap SOHO NASes mentioned before in this thread.
> Build your own from HP, Dell or IBM hardware and preferably OpenSolaris.
> (I know, sounds weird on a CentOS-list).
> For example: if your cheap "NAS"'s storage controller dies, are you sure
> that the replacement unit's controller you get can actually read the data?
> Also, if you have data on iSCSI, you really need hardware with almost no
> unplanned downtime. Even planned downtime can be difficult to manage,
> because so many servers depend on the iSCSI-targets and you'd have to
> shutdown maybe a dozen or more servers for that single reboot.
> Centralized storage is nice for management and backup, offers a lot of
> possibilities regarding efficiency and utilization - but tends to create
> single points of failure that just don't exist with direct attached storage.
> Rainer
> _______________________________________________

Hi Rainer,

I honestly don't want to spend a lot of cash on a proprietary system
like NetApp and actually want to use a lot of old tower machines (i.e.
limited space for hard drives, and no redundancy, slower CPU's, etc)
we already have. CentOS is my preferred OS of choice, and I don't know
Solaris, at all. I could probably give it a go, but not right now.

The setup I'm hoping to achieve is as follows:
We develop a lot of PHP + MySQL based intranet and internet
applications, so the main server currently runs Apache + PHP + MySQL +
Zend, etc.

Some of the applications require large volumes of data which is
currently saved on the sambas server. This makes it easy, as any one
on the LAN can add / remove data to the SMB server, and the PHP app
can also access it. But I still have a problem, that if the storage
runs out, and I add another box to the network, then it's a different
server with a new storage point - not ideal.

I was hoping with iSCSI to join these storage servers into one large
storage volume, together with XFS (or ClusterFS / GclusterFS?) and
thus have anyone connect to one "central server", both for
development, file storage and even email. Everything runs on Gigabit
switches, so that's not a problem, and redundancy isn't the highest
issue either.I'm not too concerned with that, for this particular

So, trying to use existing hardware, and preferably CentOS (I would
prefer not to reinstall the server right now), what else (if iSCSI
isn't right) would I rather use,if I want to consolidate the storage
of a few Linux machines, and export it over the LAN to various

Another project altogether though would require a similar setup with
cheap central storage server(s) at a data centre - but this will
purely be a storage server for XEN virtual machines to connect to, and
store backup data. For this OpenFiler works very well at the moment.

Kind Regards
Rudi Ahlers
CEO, SoftDux Hosting
Web: http://www.SoftDux.com
Office: 087 805 9573
Cell: 082 554 7532

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