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SAS Expander vs iSCSI SAN

I was wondering if there is any significant advantage in using a SAS Expander over an iSCSI SAN when trying to implement virtualization.

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DAS or Direct Attached Storage will be much faster than using ISCSI, especially when using database data.

You get a HBA (Host Bus Adapter) which will give you 8Gb fiber option to your SAN device if the SAN device has fiber controller.

iSCSI is usefull when users will access data accross WAN but if you need high througput you only have two choices (fiber channel) or DAS.

Depends upon what you're trying to accomplish.

SAS Expander will provide for local storage to the device that you are expanding.  If your SAS expansion chassis allows for multiple HBA connections you may be able to add another Server connection to it also.  This solution will probably only allow for 1 server though.

iSCSI storage has the benefit of being a Storage Area Network, or SAN.  A SAN is a specific type of network which allows for multiple host connections.  If you wanted to provide high availability servers as an example you can do that with a SAN, but you cannot with local storage.

What are your goals for virtualizing your equipment?

Testing on the cheap?
Production servers for less than dedicated hardware?
Mission-Critical availability of servers/services?


We are virtualizing to reduce costs and consolidate.  We are looking for High Availability but are also concerned about performance.
If you want high availability you would need a Storage Device like the MSA2000fc (HP product)
You would need two HBAs per server (for redundancy)
You would need two fiber switches (for redundancy)

The Storage device will then have two fiber channel controllers with two interfaces each.
Controler 1 Interface1 and Controler 2 Interface 1 connects to one Switch
Controler 1 Interface 2 and Controler 2 Interface 2 connect to the other Switch.

You then have two HBAs in each server connecting back to either of the switches to have complete redundancy.

on the storage device have two additional drives i.e RAID5 with one drive parity and one drive as online spare.

Distinguished Expert 2019
A SAS expander simply provides SAS fanout, for example so you can have lots of disks on a single SAS RAID controller. I think you mean SAS switch. There's a big difference.

Taking jtdebeer's example above and converting to SAS attached:

Two SAS HBAs (or a dual channel one) per server
two SAS Switches - http://www.lsi.com/storage_home/products_home/sas_switch/index.html or HP's blade SAS switch
some external SAS cables.

SAS is currently limited to a single switch, so max 4 dierct attached servers to the MSA2312sa, or 32 odd servers in a SAS switch environment. F/C was once single switch but now you can build a big fabric with them so hundreds* of servers and storage boxes on the same fabric.

(tens of thousands of servers and storage units in the biggest f/c SANs)

With iSCSI you've got 1 or 10Gb bandwidth on one cable, with f/c you've got 8Gb, with SAS you've got 12 or 24Gb (4 lanes) per cable but all these are generally higher than the speed of your disks.


andyalder: so by that logic, i must assume that it is more cost effective (read: less expensive) to decide on the iSCSI SAN solution because i'd be paying for bandwidth i would never utilize.
Distinguished Expert 2019

Depends on how much kit you already have, if you need to buy a pair of non-blocking gig ethernet switches and dual channel NICs SAS may be cheaper, if you've already got the network kit then iSCSI will be cheaper. Depends a lot on whether you want to boot from SAN or not, booting from SAS based shared storage is trivial, for iSCSI you need expensive iSCSI hardware HBAs.


We already have gig ethernet implemented in our infrastructure and i am looking to boot from SAN eventually when we expand on virtualizing our workstations.
Hi again,

Let me paint a quick picture for you.  I have a client who has 10 Guest (Server 2003) images running on 3 Host (Server 2008 R2 Enterprise) servers.  The 3 host servers connect into a very cost effective (cheap) HP MSA2000 iSCSI SAN Solution.  The performance is phenominal for their needs which include MS Exchange, 2 AD controllers, File Server, SQL Server, WSUS/Security server, Medical App Server, and a few Terminal Servers.
The Virtualization layer chosen for this network was Hyper-V which is very cost effective (free).  The Servers are all HP DL380 G6 which include some great virtualization features for comparitively low cost.  The DL360 G6 is a great product if you dont need much for dedicated local storage.

How many Servers are you looking to consolidate and what are their roles and OSs?
How many users/computers are on the network that you are building?


We are looking to consolidate 8 servers, 2 AD Controllers, 1 Exchange, 3 Application (WSUS, AV, Ghost, etc.), 1 Print and Firewall Log Server, 1 Fax Server.

We have about 75 workstations/users on our network.

Right now we are looking into utilizing Hyper-V as it is free.  My proposal is to run two Dell R610 Servers as our host machines and have the VMs stored on the Dell MD3000i iSCSI SAN.  The quote I have from Dell is around 15K, which is where my initial budget is at.  However, my supervisors brought up the idea of using SAS Expanders in lieu of iSCSI, so now I'm just trying to gauge other users' experiences/advice.

Well, in an earlier post you mentioned that you were looking to implement high availability.

Considering your budget, I would stay on track with iSCSI.  It sounds like your client/company doesn't have unlimited IT dollars but you do see the benefit from Virtualizing.  

For about $15k you could build a nice, high performance, low-cost, and expandable network based on the Dell technology you've already specified.  If you want to add capability later on you could add an additional SAN for storage Hi-Availability, or an additional Server for Server Hi-Availability.

The primary things you should be considering at this point are how you are going to back up the SAN and what happens in common disaster scenarios (ie. If 1 of the Servers went down, would you be able to run ALL of your 8 images on the single server?  Quick tip - RAM is cheap and VMs like it, buy enough to keep the network up with a single server.  Even though this is not an ideal situation, at least the employees will be able to get their work done.

My 2 cents would be to roll the Virtual network.  The benefits outweigh the costs in almost every situation where there would otherwise be underutilized equipment :)

Distinguished Expert 2019

Booting from SAN it's probably cheaper to use SAS attached as iSCSI hardware initiator much more expensive than SAS HBA. You can't boot from SAN with software initiator obviously.

MSA2300sa supports 4 hosts direct attached SAS without having to buy switches, so really cheap solution unless you want 5 hosts.
Distinguished Expert 2019

Didn't know they already had Dell kit, don't think Dell do a SAS connected storage box with 4 host ports per controller, max 2 ports AFAIK.

Just looked up price of iSCSI HBA (to boot from SAN saving cost of local disks) about $1000, SAS HBA about $200.