[CentOS] using CentOS as an iSCSI server?

Rainer Duffner rainer at ultra-secure.de
Wed Oct 21 09:36:42 UTC 2009


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


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