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iSCSI vs SAS (SMB3 vs Block Storage)

Posted on 2014-02-28
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Last Modified: 2014-03-18
Hello Folks,

We are coming up to the hardware selection for our ERP (Dynamics AX 2012 R2) implementation and we have almost chosen what we need. The shopping list is below:

P2000 (12 disks, one RAID 10 Array) [10gigbit iSCSI dual port controller -OR- 6Gigbit SAS]
2 * HP G8 (2650-v2, 64GB Ram, 2gb RAID controllers, etc.) [10Gigbit iSCSI -OR- 6Gigbit SAS]

The above servers will be in running Windows Server 2012 R2 in a two node cluster configuration with the usual back-end storage setup [iSCSI or SAS].

However, we wanted to know what would be a more appropriate setup for us.

1. 10gigbit iSCSI configuration with the complexities of IP management and Block Storage
2. 6gigbit SAS setup with standard attached storage with replication or a simple cluster

In both cases 6gig or 10gig is more then enough for the back-end bandwidth but we were mainly thinking which would be easier to run long term and more appropriate. There is no real future expansion needs and two nodes would be the maximum the setup will ever be. We are trying to keep things simple yet redundant. Does SAS require clustering?

Many thanks.
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Question by:dqnet
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Author Comment

by:dqnet
ID: 39896804
Forgot to add;
Would it be more appropriate to run Block Storage (iSCSI) or use the new Scale out Feature using SMB 3 so we just need file shares? - creating a JBOD set of disks and no RAID at P2000 hardware level.
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Expert Comment

by:Cliff Galiher
ID: 39896967
I'd go SAS, but honestly I'd want to do a full site survey before I committed to anything. This is just an off-the-cuff response given very limited information.
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Assisted Solution

by:gmbaxter
gmbaxter earned 334 total points
ID: 39897268
I would go iscsi. You may want to scale out in the future or you may even want to replicate the p2000 to another for DR. This would be harder to accomplish with sasand not as effective.
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Expert Comment

by:andyalder
ID: 39897407
SAS is actually 24Gb since there are 4 lanes but as you say bandwidth isn't a bottleneck. as gmbaxter points out SAN level replication is not available on the SAS host connect variant of the P2000 MSA. The SAS host connect version does allow clustering since the RAID controller is in the SAN, beware though that there is also a SAS interface card available to make it non-shared DAS which does not allow clustering - the price is a clue there, the SAS and iSCSI versions cost similar amount, the dumb SAS enclosure is $3000 cheaper. SAN level replication to a remote site requires additional software to manage failover although that can be also done manually.

If you are able to provide HA using local disks then that's better than a shared SAN as far as price/performance goes, but I do not know if Dynamics AX provides its own replication.

There's another option for using local disks (you can get DL380s with 25 disk bays although high wattage CPUs may be excluded due to restricted airflow), you can use a software based iSCSI SAN with replication on a virtual machine running on the same box you run AX on. Cuts down on having to buy a SAN but uses up some of the RAM and CPU of the host. VMware VSA, HP LeftHand VSA, Starwind/Starport are examples - you do have to pay for the virtual iSCSI SAN software of course.
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Assisted Solution

by:Mysidia
Mysidia earned 166 total points
ID: 39898002
SAS  IS a block storage technology;  it's just a different physical transport for the SCSI protocol.

iSCSI is  SCSI transmitted over IP instead,  normally on top of 10-gigabit Ethernet.
Using SAS to attach your block storage is the higher throughput interconnect,  but iSCSI is a more flexible,  and usually less-expensive host interconnect,  since plain 10-gig network cards are used.

SAS requires a VERY careful specialized selection of HBAs to be installed in your servers;  generally,   after buying your storage array or SAS switches, you may very well find that  server HBA's from different vendors can't even see your storage.

And it may be a nightmare, if you need to zone or map certain SCSI targets to certain hosts on your SAS switch.

I would consider  Fibre Channel  or iSCSI the mature reliable technologies for shared storage on a number of hosts, and  "SAS Attachment"   to be a minefield.



But if you specced out components for a 2 node cluster  from one vendor,  and you know 100%  certain  the cluster will never be  expanding by adding more servers or storage devices,  upgrading  storage arrays,  or adding features not supported by the SAS solution such as replication for disaster-recovery,   then SAS attach could be the way to go, for sure.
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Author Comment

by:dqnet
ID: 39900688
Thanks for all the responses.

This is exactly my issue. I am slowly moving to the iSCSI option but my worry is just the administration and headache for all the setup (assuming the SAS option is easier). Cost on the implementation is not really a worry however fiber channel is out of the question unfortunately. We definitely have the SAS route or the iSCSI route.

We wont be expanding but of course you never know (highly unlikely)

Any other inputs / opinions?

(Filling up all the drive bays with 300gb 15k drives in local raid is also an option with replication running between the servers but I just feel that since its ERP level software it should be clustered?)
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Expert Comment

by:andyalder
ID: 39901335
Just to add that the SAS variant has 4 host ports per controller so you can actually have a 4 node cluster. HP don't support it in a switched SAS environment except when the hosts are blade servers so 4 dual port directly attached hosts is the max using normal servers.
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Author Comment

by:dqnet
ID: 39902405
Fantastic responses! Thanks to all.

I am slowly leaning back to the SAS route.
Doesn't the iSCSI route also give separate links for Live Migration and VLans though?
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Expert Comment

by:Cliff Galiher
ID: 39902989
You can isolate network traffic for live migrations regardless of your shared storage being iSCSI or SAS. And live migration traffic will NOT be iSCSI either way. So no, iSCSI does not itself do anything special for live migrations (or VLANs, you'd need to set those up separately regardless as well,)
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Expert Comment

by:andyalder
ID: 39904444
One plus side for iSCSI, in your two host sscenario you can directly attach the hosts as there are two 10Gb iSCSI ports on that model, you would need 10Gb NICs though as it won't negotiate down to 1Gb even for testing. Just like SAS that wouldn't need VLANs for iSCSI because it wouldn't go through a switch.
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Author Comment

by:dqnet
ID: 39914457
@andyalder - I thought exactly the same thing. My only issue here is during out test setup it is proving to be so confusing to set up iSCSI and so difficult to run...

How are others finding it? The whole clustered services with iSCSI?
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Author Comment

by:dqnet
ID: 39926323
Anyone?
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gmbaxter earned 334 total points
ID: 39927004
iscsi is pretty straight forward. The target is the storage array, the initiator is the server.

You need to initiate the connection on each server per path, so assuming you have controller 1 and controller 2 with 2 ports each, you need to initiate controller 1 and controller 2 separately from server 1 and then repeat for server 2.

Each fault domain should have a separate subnet, for example controller 1 has 10.0.1.0/24 and controller 2 has 10.0.2.0/24

You then need to ensure that MPIO is installed on the server, and your MPIO policy is configured correctly
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Author Closing Comment

by:dqnet
ID: 39936744
Thanks folks - points assigned best way I thought..!
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