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Mirroring two servers

Posted on 2010-08-25
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Hi Guys,

We want to mirror two Windows servers.  Thus, everything (including O/S) should be mirrored from the primary (1) to the target server (2).

The two servers are the same models, drives, etc.

Purchasing software is not an issue, but we need to know what our options are to accomplish the best results.

We want a simple switch-over solution, where one would be able to switch off the primary server (1), switch on the target server (2) and everything will simply be up and running as on the primary server.
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Question by:Rupert Eghardt
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by:Mike Thomas
ID: 33519450
Sounds like you need active/passive clustering, what will the server be running?
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by:Lee W, MVP
ID: 33519467
Actually, it sounds like you're looking for a product like DoubleTake or NeverFail.  Good that price is not an issue as they are EXPENSIVE.  
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by:Rupert Eghardt
ID: 33519469
The server will be running Exchange Server 2007 mainly with some file-server roles, data- and printer sharing, etc.

The ideal is to have the PDC on a separate dedicated server.
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by:woolnoir
ID: 33519483
You best bet would be a failover cluster if the operating system is going to be windows. Get 2 machines, 2 copies of windows 2008 enterprise and a shared storage device which uses FC or Iscsi - the servers will use the shared storage for their data and when one dies the other will take over automatically....

It depends somewhat on what applications or services you will be deploying using the mirror .. clustering may not be the right choice. More info would help.

Might b worth reading here

http://technet.microsoft.com/en-us/library/cc731844(WS.10).aspx
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by:Rupert Eghardt
ID: 33519489
Hi Leew, are these packages readily available at distributors, or should it be purchased from the net?
I remember a while ago, I saw documenation about a Symantec product that was also design to do this, but not so how effective it will be, as Symantec EPP has been somewhat dissapointing lately.
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by:woolnoir
ID: 33519492
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by:Lee W, MVP
ID: 33519515
I loath symantec, so I wouldn't go with them.  

I don't know the availability of those products - other than Sunbelt Software partners are authorized distributors of DoubleTake (I was able to sell a couple to a client).
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by:Rupert Eghardt
ID: 33519555
Yes, this could cover the Exchange replication and fail-over.
It would be ideal to have a replica of the whole server for instant automatic fail-over.
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by:Lee W, MVP
ID: 33519626
Instant is not happening with DoubleTake or likely NeverFail.  They would take 15-60 minutes depending on how much has to fail over.  But what happens is the second server takes over literally and FULLY for the failed server.

For Exchange Failover, you'll likely be looking for either an Exchange Cluster and CCR or a non-cluster and LCR - more info here:
http://blogs.technet.com/b/scottschnoll/archive/2006/10/06/exchange-2007-_2d00_-continuous-replication-architecture-and-behavior.aspx?wa=wsignin1.0
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by:woolnoir
ID: 33519666
yeah i dont think whole server replication is going to work the way you imagine. You may want to consider something like VMWARE and have the VM running across two physical boxes. ESX server offers the ability to migrate a server across two VMware HOSTS but again you need shared storage to allow that

VMware would also give you more flexibility in terms of the actual server images as you could hold snapshots for quicker restoration if needed as well as the above migration between hosts.
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by:Rupert Eghardt
ID: 33519783
Could VMWare run over two boxes at the same time (like in a RAID config), should the one box disappear the WMWare will automatically balance the load off the other (single) box?
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by:Lee W, MVP
ID: 33519854
If you have a SAN, then both VMWare and HyperV should be able to provide redundancy where if one physical server fails, the other takes "ownership" of the failed VM and keeps the system running.  This COULD be potentially near instant.
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by:woolnoir
ID: 33520086
I'd say myself and leew indicated, VMware would be the way to go for your requirements.
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by:SysExpert
ID: 33522734
I agree that a VMWare solution is going to be the most flexible, but not necessarily the most cost effective, unless you use if for other servers as well.

I think you will need the advanced or enterprise package with Vmotion and full management

http://www.vmware.com/vmwarestore/vsphere_purchaseoptions_support.html

I hope this helps !
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by:D_Vante
ID: 33532046
Virtualize and use a SAN, then make the SAN do the work of keeping a live copy
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by:Rupert Eghardt
ID: 33532340
Please give more details for setting up a SAN?
What are the requirements?
Benefits and drawbacks?
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by:D_Vante
D_Vante earned 100 total points
ID: 33532788

Benefits:
  * Host server dies, any other host server can fireup that virtual machine.  So you could have several host machines that are out of warranty
  * SAN can do snapshots in time
  * SAN can make copies of virtual machines to do testing on (patch testing etc)
  * Most SANs can also maintain copies for SQL and Exchange data (extra $$ for module)
  * One host server can run several virtual machines
  * Server becomes corrupt, roll back to your last snapshot
Drawbacks:
  * Price
  * You need to have a good service agreement on your SAN because you can not go to a local store and buy a power supply, HD, controller card, but usually everything is redundant on a SAN or you can spend more money and have another SAN to backup to.

 Depends on how much $$ you have and critical is it to have a good failover plan

 
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by:Lee W, MVP
ID: 33532969
SAN = Storage Area Network:
http://en.wikipedia.org/wiki/Storage_area_network

My summary:
A SAN is Shared storage that can be accessible to multiple servers and "partitioned" to be used by multiple servers.  SANs are often used in failover cluster environments where you need to have a central storage location.  One server typically has "ownership" of a block of storage on the SAN.  When that server fails, the other automatically and near instantly (Within seconds) takes over for it, assuming ownership of the cluster name and resources.
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by:woolnoir
ID: 33533119
Have a look into some ISCSI SAN's or attached storage devices. They need to be windows 2008 compatible if you will use hyperV, vmware should maintain their own list. Then you need two servers, again from the VMware supported HCL. You can then configure the WM's to be portable between the hosts and VMWARE can auto failover, it uses the SAN(iSCSI or Fibrechannel) to storage the images (VM's and disks).
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by:woolnoir
ID: 33533146
@D_Vante its not the SAN that controls the snapshots, or makes copies of VM's the SAN is used by the VMWARE or HyperV host machines to do those operations.

HyperV or VMWARE can do snapshots, they can do rollbacks, they control the SAN which stores the VM's and virtual disk images. The SAN is nothing more than a fabric of storage units, there is very little in terms of intelligence in most (though some do have more than others.)
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by:D_Vante
ID: 33533259
Yes, the host can do the snapshots as well but the SAN can do it too.
http://www.compellent.com/Products/Software/Continuous-Snapshots.aspx
 
 
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by:woolnoir
ID: 33533317
@D_Vante ; note the fact that the link you have posted is in the 'software' section - its not the Hardware that has the intelligence to do it. Its semantics, not worth the discussion, i just dont want people being confused thinking that most sans offer a magical ability to autosnapshot. When used in a hyperV or VMware situation its the hypervisor i.e the VMWARE or hyperV system itself that manages the online snapshots so their is no interruption to operation.
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by:D_Vante
ID: 33533513
@Woolnoir;  Yes your are correct it is software.    I guess what I am trying to say here is the software is run on the SAN.  
   Also, to enable features many SAN vendors sell them in modules, which means you need more $$$.   One of my clients has Equalogics installed and with them you get all the modules and updates as well.
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by:Lee W, MVP
ID: 33533526
D_Vante is correct.  High-end SANs have been offering Snapshot features long before VMWare existed and Windows had any such feature.  Smaller, cheaper SANs do not offer the feature.  And the compatibility of the SAN based snapshot feature with a VM technology MAY be questionable, but for typical files, it's just as effective as Volume Shadow Copy - and in some ways, better.

(Products like those from EqualLogic (now Dell) offered this feature).
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by:woolnoir
ID: 33533557
Yes, 'high end' , my point was i'm not thinking of a high end unit, more a low-> mid range tray sized storage unit that can be used for a low cost VMWARE solution. I didnt want to start drifting away from the original issues and so wanted to keep some handle on cost.

>And the compatibility of the SAN based snapshot feature with a VM technology MAY be >questionable, but for typical files, it's just as effective as Volume Shadow Copy - and in some >ways, better.

Given the fact we are talking about the ability of VMWARE to do machine snapshots and portability, the fact that you agree about questionable compatibility is my point, i didnt want to muddy the waters.

I dont want to come across as discounting ideas, but i'm trying to be biased towards usable solutions at least as far as i see them.
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by:woolnoir
ID: 33533573
Any way, i think its a workable solution for the original problem, not sure what the poster thinks :)
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by:woolnoir
ID: 33533618
@leew @D_Vante my apologies if i came across as 'snappy' today, been a bad day at work, need to de-stress before EE'ing i think :)
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by:Lee W, MVP
ID: 33533620
We've long since drifted away from the original question which was server mirroring.  We're now talking about Virtual Machines and SANs.  
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by:Rupert Eghardt
ID: 33533755
Thanks Guys, no worries ... the discussion actually helped me to get a much clearer picture :-)
In other words, SAN actually comes as a unit?
It is not something that I could configure over 3 x of my own servers?
Are we talking about SAN hardware?
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by:woolnoir
ID: 33533804
SAN's are all different beasts, you can get one that is racks of disks with a controller within, you can get one the size of a shelf made of standard drives in a unit. At the low end you have something like this http://www.drobo.com/products/droboelite.php, at the other end of the scale it can be two or three orders of magnitude more expensive... depends on your needs.

I'm sure leew can give some examples of the higher end stuff, my experience of high end SAN's is 18 months old... an age in this industry.

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by:Lee W, MVP
ID: 33533864
My experience is actually older - EqualLogic ~4 years ago and Dell/Clariion ~10 years ago running a 2000 cluster.

But I do try to stay up on technology when I can.

If you want to do this right, you want quality hardware from a vendor who can give you at least 4 hour support and a 3 year+ warranty/service contract.  If you are just playing around, there are plenty of cheap/free solutions you can experiment with first to get an idea about the technology and move forward from there.  As with any major project, I recommend gaining some basic experience first - with a system like this, Hyper-V and VMWare ESXi being free, you can use products like FreeNAS that offer iSCSI host abilities.  With that, you can create an iSCSI SAN and see how things work - get an idea of the failover time and the like.  Once you know what the technology can do, you can solicit the larger vendors for solutions or hardware quotes.
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by:Rupert Eghardt
ID: 33533948
Thanks woolnoir, I reviewed the link.

These units come with more than one drive installed, for example the Elite has 8 x iScsi drives.
What happens if one of the drives actually crashes inside?
Does it have some sort of build-in RAID?

Should it be more reliable than RAID?

I had a RAID-5 config crashing a few years ago because of one drive that failed as part of the RAID.
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by:D_Vante
ID: 33534115
@woolnoir, no worries as well, this has turned into a good discussion
SANs have all kinds of RAID and tiers and even different drive types in a single SAN.  Most of the time you can only get the SAN full loaded with drives.  Then there is also the discussion of fiber vs iscsi, SATA vs SAS and IOPs  
@rupertvz, what are your thoughts so far?
 
 
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woolnoir earned 400 total points
ID: 33539796
These units come with more than one drive installed, for example the Elite has 8 x iScsi drives.
What happens if one of the drives actually crashes inside?
Does it have some sort of build-in RAID?
Should it be more reliable than RAID?
I had a RAID-5 config crashing a few years ago because of one drive that failed as part of the RAID.

-----------------

The droboelite units come with Raid6 - meaning 2 drives can fail without effecting its operation, statistically one drive will fail and on a raid5 that's the danger point, this system allows one drive failure and a more 'relaxed' repair than raid 5 would allow. The drobo units also allow more flexible expansion, you can remove ONE drive, throw in a larger one and that capacity is available - traditional raid is always based on the capacity of the smallest drive, i.e smallest capacity x number of drives -1 (generally).
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by:woolnoir
ID: 33553624
Did the above answer your questions, or did you want more info/discussion, just need to know if i should keep track of this Q :)
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Author Closing Comment

by:Rupert Eghardt
ID: 33768181
Thanks Guys,
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