Replication with an EqualLogic SAN; Part 3

 

In parts one and two of my journey in deploying replication between two EqualLogic PS arrays, I described some of the factors that came into play on how my topology would be designed, and the preparation that needed to occur to get to the point of testing the replication functions. 

Since my primary objective of this project was to provide offsite protection of my VMs and data in the event of a disaster at my primary facility,  I’ve limited my tests to validating that the data is recoverable from or at the remote site.   The logistics of failing over to a remote site (via tools like Site Recovery Manager) is way outside the scope of what I’m attempting to accomplish right now.  That will certainly be a fun project to work on some day, but for now, I’ll be content with knowing my data is replicating offsite successfully.

With that out of the way, let the testing begin…

 

Replication using Group Manager 

Just like snapshots, replication using the EqualLogic Group Manager is pretty straight forward.  However, in my case, using this mechanism would not produce snapshots or replicas that are file-system consistent of VM datastores, and would only be reliable for data that was not being accessed, or VM’s that were turned off.  So for the sake of brevity, I’m going to skip these tests.

 

ASM/ME Replica creation.

My ASM/ME replication tests will simulate how I plan on replicating the guest attached volumes within VMs.  Remember, these are replicas of the guest attached volumes  only – not of the VM. 

On each VM where I have guest attached volumes and the HITKit installed (Exchange, SQL, file servers, etc.) I launched ASM/ME to configure and create the new replicas.  I’ve scheduled them to occur at a time separate from the daily snapshots.

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As you can see, there are two different icons used; one represents snapshots, and the other representing replicas.  Each snapshot and replica will show that the guest attached volumes (in this case, “E:\” and “F:\” )  have been protected using the Exchange VSS writer.  The two drives are being captured because I created the job from a “Collection” which makes most sense for Exchange and SQL systems that have DB files and transaction log data that you’d want to capture at the exact same time.  For the time being, I’m just letting them run once a day to collect some data on replication sizes.  ASM/ME is where recovery tasks would be performed on the guest attached volumes.

A tip for those who are running ASM/ME for Smartcopy snapshots or replication.  Define in your schedules a “keep count” number of snapshots or replicas that fall within the amount of snapshot reserve you have for that volume.  Otherwise, ASM/ME may take a very long time to start  the console and reconcile the existing smart copies, and you will also find those old snapshots in the “broken” container of ASM/ME.    The startup delay can be so long, it almost looks as if the application has hung, but it has not, so be patient.  (By the way, ASM/VE version 2.0, which should be used to protect your VMs, does not have any sort of “keep count” mechanism.  Lets keep our fingers crossed for that feature in version 3.0)

 

ASM/ME Replica restores

Working with replicas using ASM/ME is about as easy as it gets.  Just highlight the replica, and click on “Mount as read-only.”  Unlike a snapshot, you do not have the option to “restore” over the existing volume when its a replica.

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ASM/ME will ask for a drive letter to assign that cloned replica to.  Once it’s mounted, you may do with the data as you wish.  Note that it will be in a read only state.  This can be changed later if needed.

When you are finished with the replica, you can click on the “Unmount and Resume Replication…”

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ASM/ME will ask you if you want to keep the replica around after you unmount it.  To keep it, uncheck the box next to “Delete snapshot from the PS Series group…”

 

ASM/VE replica creation

ASM/VE replication, which will be the tool I use to protect my VMs, took a bit more time to set up correctly due to the way that ASM/VE likes to work.  I somehow missed the fact that one needed a second ASM/VE server to run at the target/offsite location for the ASM/VE server at the primary site to communicate with.  ASM/VE also seems to be hyper-sensitive to the version of Java installed on the ASM/VE servers.  Don’t get too anxious on updating to the latest version of Java.   Stick with a version recommended by EqualLogic.  I’m not sure what that officially would be, but I have been told by Tech Support that version 1.6 Update 18 is safe.

Unlike creating Smartcopy snapshots in ASM/VE, you cannot use the “Virtual Machines” view in ASM/VE to create Smartcopy replicas.  Only Datastores, Datacenters, and Clusters support replicas.  In my case, I will click  “Datastores” view to create Replicas.  Since I made the adjustments to where my VM’s were placed in the datastores, (see part 2, under “Preparing VMs for Replication”) it will still be clear as to which VMs will be replicated. 

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After creating a Smartcopy replica of one of the datastores, I went to see how it looked.  In ASM/VE it appeared to complete successfully, and in SANHQ it also seemed to indicate a successful replica.  ASM/VE then gave a message of “contacting ASM peer” in the “replica status” column.  I’ve seen this occur right after I kicked off a replication job, but on successful jobs, it will disappear shortly.  If it doesn’t disappear, this can be a configuration issue (user accounts used to establish the connection due to known issues with ASM/VE 2.0), or caused by Java.

 

ASM/VE replica restores

At first, ASM/VE Smartcopy replicas didn’t make much sense to me, especially when it came to restores.  Perhaps I was attempting to think of them as a long distance snapshot, or that they might behave in the same way as ASM/ME replicas.  They work a bit  differently than that.  It’s not complicated, just different.

To work with the Smartcopy replica, you must first log into the ASM/VE server at the remote site.  From there, click on “Replication” > “Inbound Replicas” highlighting the replica from the datastore you are interested in.  Then it will present you with the options of “Failover from replica” and “clone from replica”  If you attempt to do this from the ASM/VE server from the primary site, these options never present themselves.  It makes sense to me after the fact, but took me a few tries to figure that out.  For my testing purposes, I’m focusing exclusively on “clone from replica.”  The EqualLogic documentation has good information on when each option can be used.

When choosing “Clone from Replica” it will have a checkbox for “Register new virtual machines.”  In my case, I uncheck this box, as my remote site will have just a few hosts running ESXi, and will not have a vCenter server to contact.

image

 

Once it is complete, access will need to be granted for the remote host in which you will want to try to mount the volume.  This can be accomplished by logging into the Group Manager of the target/offsite SAN group, selecting the cloned volume, and entering CHAP credentials, the IP address of the remote host, or the iSCSI initiator name. 

image

 

Jump right on over to the vSphere client for the remote host, and under “Configuration” > “Storage Adapters”  right click on your iSCSI software adapter, and select “Rescan”  When complete, go to “Configuration” > “Storage” and you will notice that it the volume does NOT show up.  Click “Add Storage” > “Disk/LUN”

image

 

When a datastore is recognized as a snapshot, it will present you with the following options.  See http://www.vmware.com/pdf/vsphere4/r40/vsp_40_iscsi_san_cfg.pdf for more information on which option to choose.

image

 

Once completed, the datastore that was replicated to the remote site and cloned so that it can be made available to the remote ESX/i host, should now be visible in “Datastores.” 

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From there just browse the Datastore, drilling down to the folder of the VM you wish to turn up, highlight and right click the .vmx file, and select “Add to inventory.”  Your replicated VM should now be ready for you to power up.

If you are going to be cloning a VM replica living on the target array to a datastore, you will need to do one additional step if any of the VM’s have guest attached volumes using the guest iSCSI initiator.  At the target location, open up Group Manager, and drill down to “Replication Partners” > “[partnername]” and highlight the “Inbound” tab.  Expand the volume(s) that are associated with that VM.  Highlight the replica that you want, then click on “Clone replica”

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This will allow you to reattach a guest attached volume to that VM.  Remember that I’m using the cloning feature simply to verify that my VM’s and data are replicating as they should.  Turning up systems for offsite use is a completely different ballgame, and not my goal – for right now anyway.

Depending on how you have your security and topology set up, and how connected your ESX host is offsite, your test VM you just turned up at the remote site may have the ability to contact Active Directory at your primary site, or guest attached volumes at your primary site.  This can cause problems for obvious reasons, so be careful to not let either one of those happen.  

 

Summary

While demonstrating some of these capabilities recently to the company, the audience (Developers, Managers, etc.) was very impressed with the demonstration, but their questions reminded me of just how little they understood the new model of virtualization, and shared storage.  This can be especially frustrating for Software Developers, who generally consider that there isn’t anything in IT that they don’t understand or know about.  They walked away impressed, and confused.  Mission accomplished.

Now that I’ve confirmed that my data and VM’s are replicating correctly, I’ll be building up some of my physical topology so that the offsite equipment has something to hook up to.  That will give me a chance to collect some some statistics on replication, which I will share on the next post.

21 Responses to Replication with an EqualLogic SAN; Part 3

  1. Rob says:

    Nice write-up, thanks for taking the time. You are doing something similar to what we plan, however, I have some issues with the WAN replication. At this point it would be great to have replication hardware, but we are in no position budget-wise to go that route.

    • ITforMe says:

      Thank you for the kind words. …Yeah, I hear ya on that one. You can have say, 9 out of the 10 pieces of the puzzle, but if one of them is missing (bandwidth, or a sight to replicate to, a replication technology, etc.), it becomes nearly impossible to do.

  2. Bill says:

    Great Information!! Thank you for spending the time and sharing!

    I have a question for you to make sure I’m clear on your terminology, when you say “the guest attached volumes within VMs” do you mean your VMs OS volume(ie W2k3 OS/Exchange) is a VM datastore but a Data volume(ie. Exchange Databases) connects via an iSCSI volume via MS iSCSI initiator and not just another VM datastore?

    Hope that my question makes sense.. I’m looking to re-engineer how we are doing such things in almost the exact environment.

    Thanks

    • ITforMe says:

      Hi Bill,

      Good question. Yes, that is exactly what I mean. The VM’s primary OS partition sits in a VMFS volume just like any other VM. But the data volumes for a particular VM (e.g. Exchange, SQL, etc.) are created in the Equallogic group manager, then the OS within that VM attaches to those volumes via the guest iSCSI initiator. When you do this, you get to fully exploit the benefits of ASM/ME, which is such a great tool. It works well for local snapshots, as well as replication. Now, in order to make them work as desired, I had to take the other steps I mentioned in the articles, but they’ve been working beutifully since then.

      Let me know if you have any more questions. I’ll be happy to clear up what I mangled in my blogs.

  3. Bill says:

    Thanks for clearing that up for me.. I thought that’s what you were saying but wanted to be clear.

    I’m the new net admin here and Exchange 2007 is virtualized but the OS/Mailbox Databases/Logs are all on one VMFS volume on the Equallogic, so this is a challenge to get this squared away correctly. They were simply replicating this volume hourly off-site, but from what I understand it isn’t that easy… I’m looking to reconfigure this and do it “right” this time around. Utilizing the 3 PS SANs we currently have to backup our VMs & data cost-effectively.

    I’m continuing to dig into this…… fun fun!!

    • ITforMe says:

      Happy to know these are helping someone.

      Yeah, it sounds like you are going in the right direction. Pulling them out as vmdk’s sitting in a VMFS volume, over to a guest attached volume really offers up so much flexibility for you. One of the many side benefits is that it takes a burden off of your VMFS connections, and makes snapshots of the data super fast (the VSS writer does this much more quickly than a fully encapsulated VM snapshot). ASM/ME really shines when you get it working, and can come into play whenever there is a VSS writer involved (NTFS, SQL writer, Exchange writer). The big thing for me was getting ASM/VE and ASM/ME to play nicely with respect to how they differ in processing snaps and replicas, respectively. But I think I documented just about everything I could think of at the time, so the info you are looking for should be buried in there somewhere.

  4. Pingback: Customer Blog: EqualLogic Replication in Detail « Marc's thoughts on Dell EqualLogic

  5. Mark says:

    Since ASM/VE 3.x is a vCenter plug-in now my guess is you now require a licensed vCenter at each location.

    • ITforMe says:

      The documentation for ASM/VE 3.x certainly implied this, as they omitted any scenario in which one did not have vcenter at the remote/target location. However, I did confirm with their engineering team that it will work without an instance of vcenter running remote/target location. At the heart of it, even in 3.x, ASM/VE is still a couple of web services running at their respective locations. Hopefully they will clear up this particular scenario in future editions of their documentation.

  6. Ollie says:

    What a brilliant blog! Really helped me get this up and going for my company thanks! Only question I have is how do i limit the number of replications that are kept. I only want to keep to at any time?

    Thanks
    O

    • ITforMe says:

      Thanks! It’s comments like yours that keep me going. Anyway, to answer your question, it kind of depends.

      1. If you are using ASM/ME, you can easily set/limit the number of replicas (via the “keep count”) option. This mechanism works the same for SmartCopy Snapshots, and SmartCopy replicas.
      2. In ASM/VE 2.x, there is no mechanism for specifying a keep count. When it runs out of room, it will just remove the oldest snap or replica. In ASM/VE 3.x (not available at the time that I created the series of posts).
      3. If you are making snaps or replicas via the Group Manager, there is no mechanism for keep count. But this isn’t much of a hinderance, since creating snaps or replicas this way should be very limited.

  7. dave says:

    Interesting articles to read. a lot of value in it thank for that!
    But I’m still wondering if for ex you put your exchange server in a vmfs volume and you use ASM/VE to make a smart replica are they 100% consistent or is it better to use windows to connect to an iscsi volume on your san to put your data on it. And then use ASM/ME to use smart replicas?

    • ITforMe says:

      In the case of Exchange, SQL, or files that require signifigant coordination in I/O (via VSS), it is absolutely better to use ASM/ME with guest attached volumes. If you didn’t do this, and you relied on ASM/VE to protect the system (C:\) and other VMDK files that would be where your Exch DB and TL live, it would make a hypervisor consistent snap, but it wouldn’t do any coordination of file system I/O with VSS. The goal here of course is to make a snap or replica that the application itself is going to like. That really means leveraging VSS when the machine is on and running. ASM/ME with guest attached volumes is the way to do that.

      Did that answer your question?

  8. dave says:

    That’s what I’m also been hearing but if you should believe vmware, they say that since vsphere 4.1 the snapshots fully support VSS.
    Do you have any experience with that?

    • ITforMe says:

      Great question Dave. It’s actually a pretty complicated answer. It really depends on what version of OS and hypervisor is being run, and what particular VSS writers it is supporting at that given moment. This link: http://www.veeam.com/blog/the-great-vss-debate.html provides some good information, and even thought it is from a commercial backup vendor, it takes into consideration how complex the question of whether is something really using VSS or not. I look for the answer to get easier as time progresses, and the hypervisor and OS versions are more sophisticated, and willing to coordinate actions with eachother.

  9. sean trimm says:

    There is the implication that it is possible to replicate Smart Copies through ASM/VE without the use of a second vcenter installation.
    Can you please tell me if you have implemented the HIT 3.01 in this manner?

    Thank you,

    • ITforMe says:

      The key to this is understanding that even with the new version, it just references a URL (just as it did with the old version). So it will imply vcenter registration, but it is not necessary.

  10. stu says:

    Hi Great post,

    I would like to find a little more information on ASM/VE not requiring a second vCenter on the fail over site, could you point me at any doc’s?

  11. source says:

    How come you do not have your web site viewable in wap format? Can not see anything in my iPhone.

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