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What is VSAN? What's so different about it?

Posted on 2015-01-02
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hi guys

i'm looking at the pluralsight.com training videos on VSAN's. And none of these videos explain precisely what is so different or great about the VSAN?! Everything is so abstract 'it is fully integrated into Vmware vsphere.....it is part of the Vsphere hypservisor....it consists of policy based storage'. There's no explanation in basic terms.

We use a Vmware environment with datastores and we're using Vsphere 4.1. What is so different about it than the VSAN offered in 5.5? What does the VSAN do? How does one really take advantage of it in a real world scenario?

Thanks for your help and a happy new year
Yash
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Question by:Yashy
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Andrew Hancock (VMware vExpert / EE MVE) earned 350 total points
ID: 40528457
This is not to be confused with the previous VMware vSphere product VMware vSphere Storage Appliance (VSA), which is based on a Virtual Appliance hosted on VMware vSphere (ESXi).

VMware Virtual SAN (vSAN) is built into the VMware vSphere (ESXi) 5.5 vSphere kernel. Both VSA and vSAN are similar in concept; they are both virtual but their similarities end there. vSAN provides better scalability, resilience and availability than VSA, (vSA does not scale beyond 3 hosts), and vSAN scales out better for virtualized/cloud environments, it's aimed at the Enterprise or Commercial vSphere customer. vSAN requires a minimum of three hosts for deployment, and supports SSD read and write buffering (caching). At least one SSD and one conventional magnetic hard disk drive are required per host for deployment (1 SSD, 1 HDD per host x 3 minimum). SSD caching is not supported in VSA. You cannot at present use all SSDs for a vSAN.

It's locally attached storage to an ESXi host, which is mirrored between hosts!

So it does not have the network performance issue, of a traditional SAN, either FC, iSCSI or NFS, because it's Direct Attached Storage e.g DAS.

Also employs low cost SSDs, for Read and Write Cache, and can use slower HDDs

and finally, it's "mirrored" between all hosts, so if one host fails, it's still up!

That is what vSAN is!

I've created an EE Article, with a quick explanation of what vSAN is!

HOW TO: Set up a lab environment for vSAN using VMware Workstation

http://www.vmware.com/uk/products/virtual-san
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by:arnold
arnold earned 150 total points
ID: 40528471
vsan is a virtual SAN (storage Array Network)
VMWARE has a writeup on it at http://www.vmware.com/products/virtual-san
A detailed write is further included below
http://www.vmware.com/files/pdf/products/vsan/VMware_Virtual_SAN_Whats_New.pdf

Deals with having virtualised shared storage for often needed technologies as clusters from member hosts.

I.e. Do you currently have a SAN outside your VMWARE environment?
The write up covers the scenario in greater detail, but lets say you have three vsphere hosts meeting the vsan requirements.
Each has 10 fixed disks
The vsan allows for the combination of the 10 disks of each host into a combined storage resource.
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by:gheist
ID: 40528826
Usually one has some NAS on the network or SAN. vSAN is so special that it uses ESXi hosts local storage to provide highly resilient storage across your vmware infrastructure.
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by:Yashy
ID: 40528969
Thanks for the feedback everyone.

Here's what I am grasping so far:

So currently, if I have an Esxi host with just two disks (usually just used to install the OS), I would expand the local storage to around 6 with (as an example) 1TB each and that storage would be usable across my other Esxi hosts?
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Note quite correct, usually you would not install the OS on any disks, leaving all the storage for datastores.

You would have to install 1 x SSD and 1 x HDD per host at least, using three hosts! So 3 SSDs and 3 HDDs MINIMUM and 3 Hosts!

vSAN is also licensed per CPU in the Host!

It's not cheap! So three dual processor hosts, that's 6 x vSAN licenses required!

BUT, the difference is this local storage is "mirrored and combined" from 3 hosts minimum to all hosts in the Cluster.

It's local direct attached storage so faster access, BUT, you must have at least 1 SSD (or SSD flash card) and 1 traditional hard drive per host to create a vSAN.

You cannot create a vSAN with just magnetic disks, e.g. SATA or SAS!

Traditionally, you would access a SAN via your network or FC network.

This is local....

See my EE Article I posted, which shows how easy it is to create!
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by:Yashy
ID: 40529006
Aha okay, i get it.

We have 6 x IBM x3650 M3 servers used as Esxi hosts currently. I think each of those has around 7 or 8 available slots for disks.

Under our current circumstances, does that mean that if  we added more storage to those Esxi hosts, then none of the storage would be available to the cluster unless we upgraded to 5.5 and had were licenses for using VSAN?


Also:

1. Surely in terms of disk space we would be limiting ourselves? Would a SAN that's attached and has 100 disk slots not benefit in the longer term for storage?

2. How much of a difference would the I/O read/writes of the local attached storage make in comparison to a conventional SAN that's attached with fibre links?
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ID: 40529032
Under our current circumstances, does that mean that if  we added more storage to those Esxi hosts, then none of the storage would be available to the cluster unless we upgraded to 5.5 and had were licenses for using VSAN?

Correct, and you would need to purchase a minimum of 3 x SSDs for the hosts.

1. Surely in terms of disk space we would be limiting ourselves? Would a SAN that's attached and has 100 disk slots not benefit in the longer term for storage?

Yes, but it depends on how many IOPS and Performance you require for your VMs!

Think of tiered storage, and different datastores for different VMs, and their performance requirements.

2. How much of a difference would the I/O read/writes of the local attached storage make in comparison to a conventional SAN that's attached with fibre links?

Remember it's not just local. storage it's also Read and Write Cache using SSDs, far greater.

2 millions IOPS have been quoted and benchmarked using vSAN.
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