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Moving to NAS storage

Posted on 2010-09-23
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Last Modified: 2012-06-21
Hi

We have several applications that run on ESX 3.5. The guest OS is Windows 2003 SP2. At the moment, all our ESX hosts are SAN attached.

We've just bought a NAS too and will be building ESX 3.5 servers that are NAS attached too. We'll be building more application servers on the NAS attached infra too.

From a guest point of view, is there any difference between NAS and SAN hosted servers? Is there a difference in I/O etc?

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Question by:bruce_77
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Dangle79 earned 167 total points
ID: 33746618
Kind of depends on whether you're using fiber channel or iscsi.
with the former you're looking at transfer speeds of 4Gb and up, the latter you're limited to your LAN speed. When it comes down to the hardware I/O a NAS is typically going to be slower than SAN
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by:bruce_77
ID: 33746636
Thanks!

Sorry, I'm not a storage person! fc and iscsi refer to the NIC technology? And why is NAS slower in terms of I/O than SAN?
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by:Dangle79
ID: 33746689
SAN is built to be used for high performance and reliability, NAS devices are generally nothing more than a RAID set that plugs into your network to drop files on.

FC runs dedicated while iscsi can go either way. some people build dedicated networks to do iscsi, while others just run it over their existing LAN segment.
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by:BloodRed
BloodRed earned 167 total points
ID: 33747253
FC is a dedicated fiber network specifically used for storage and can make use of FC switches, which allow you to do zoning and masking.  It comes in speeds of 2 or 4 GB, you see FC in dedicated storage area networks.  It is more expensive due to the dedicated hardware and HBAs.  It also generally supports multipathing natively and is required for some types of advanced virtualization use cases.

iSCSI is SCSI signaling over an ethernet network, it is limited to the speed and throughput of your networking hardware.  It was thought of as lower end traditionally, but with the wider availability of 10GbE it is becoming more widely used.  

Anyway, both types of datastores are mounted directly to the ESX host and presented to the VMs as local SCSI or IDE storage, so from the VM's point of view there is no different.    
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by:bruce_77
ID: 33747989
Thanks...

So you could say that NAS and SAN were the storage technology, whereas FC/iSCSI is the network technology?

So with FC you have an entire network based on FC switches and fiber cables?

Whereas with iSCSI you use general networking (e.g. Cisco) hardware and normal ethernet cables? It basically uses the IP network?

And both NAS and SAN can support either FC or iSCSI? Are there any other types of network?
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by:Dangle79
ID: 33748063
you're 90% correct. i've never seen a NAS that supported FC. doesn't mean it's not out there.
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by:bruce_77
ID: 33748127
So can NAS only use iSCSI? Are there any other technologies it can use?
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by:Dangle79
ID: 33748161
NAS is typically just TCP/IP although you can implement iscsi with software
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by:BloodRed
ID: 33748181
There are hybrids, like NetApp filers which can support FC, iSCSI, NFS and CIFS all from one head.  So they are distinct technologies but some devices support all at once.  Of those, all are ethernet-based and traverse a standard TCP/IP network except FC, which requires non-standard hardware.
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by:bruce_77
ID: 33748199
Thanks Dangle.

To summarize, the differences we would see:

1. SAN performs better to NAS in terms of disk I/O performance (speed?)

2. Since NAS generally doesn't use FC, data transfer speeds (between where and where - the client and the server? Or between disks on the NAS) are slower?
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by:Dangle79
ID: 33748323
1. yes, generally speaking
2. FC is the network between the client/server, switches, and storage heads
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by:paulsolov
paulsolov earned 166 total points
ID: 33749674
Typically a SAN is block based storage (FC, iSCSI) and NAS is NFS is a vmware environment.  What type of NAS are you getting with what type of drives (you calculate IOPS based on types of drives and number of them).  The rest depends on throughput but you can use trunking, MPIO, etc..

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