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  1. VCDX in 2017 Essendon's Avatar
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    #151
    Quote Originally Posted by jibbajabba View Post
    SRM5.0 is simply not aware of the location of the VM once moved.

    I remember big outcries back in the day. I remember it was originally supported but then quickly changed to not supported.
    And this exactly why I encourage the use of permissions that disallow admins from chucking VM's/vmdk's wherever they feel like.
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  3. VCDX in 2017 Essendon's Avatar
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    #152
    You are likely aware of it already Tom, the SRA detects replicated LUN's and they show up in the Datastore Groups area in SRM for you - it doesnt actually replicate the LUN's, that's done by your arrays' replication mechanism.
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  4. Senior Member tomtom1's Avatar
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    #153
    Quote Originally Posted by Essendon View Post
    You are likely aware of it already Tom, the SRA detects replicated LUN's and they show up in the Datastore Groups area in SRM for you - it doesnt actually replicate the LUN's, that's done by your arrays' replication mechanism.
    Actually, no I wasn't. I don't have hands on with SRM, either in the lab or in production. Perhaps something to look at a bit later on..
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  5. VCDX in 2017 Essendon's Avatar
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    #154
    Question 24

    Well we know that Dorothy has lost her job and due to the natural disaster the company doesnt have any money just yet to hire a new vAdmin. One of the company's systems administrator is tasked with recovering data from tape (thank God for tapes, the company will be able to recover their data albeit with the significant outage). The last known good backup was taken 8 hours before the cyclone hit the primary datacenter. The amount of time the business can be without their services without incurring significant losses is 6 hours. It's been estimated it would take 4 hours for them to recover lost data, recover from backlog and verify operational services.

    - What are the RTO, RPO, Work Recovery Time and Maximum Tolerable Downtime values?

    - What could've been done to have more recent data available?

    - The RPO seems to be determined by the time it takes to take a full backup. What should it be determined instead by?

    - The admin now responsible for recovering data from tape has suggested synchronous replication for all LUN's so no data is ever lost. Has he taken into account the fact that the secondary datacenter is in a city about 30 kms. away. What are some of the other considerations this dude needs to take into account?
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  6. Senior Member tomtom1's Avatar
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    #155
    RTO = The amount of time, usually in hours that is needed for the business to restore itself to the last available point of restore (RPO). In this case, the time needed to restore has been determined to be 4 hours.
    RPO = The amount of time, usually in hours, a backup may old. In this case, the RPO has been determined to be 8 hours.
    MTD = The amount of time, usually in hours, the business may lose the business services and still recover from this. MTD = 6 hours
    WRT = The amount of time the business needs to fully recover from the disaster, after having restored the data from the RPO, in the time specified by the RTO. The fact that the IT services have been restored after the disaster, do not mean that the business is fully operational again. The WRT would be 2 hours.

    The sum of MTD = RTO + WRT.

    What could have been done to have more recent data would be to decrease the RPO period. That would mean backups would be made more frequently and (more) recent data is available in the event of a failover. RPO and RTO values should always be primarily driven by business requirements. A technical solution should adhere to business requirements, and not the other way around.

    When the technical solution does not meet the business requirements, this could also be interpreted as a risk, and therefore needs to be mitigated.

    When the other admin is doing synchronous replication, he should consider these factors:
    • Latency
    • Distance
    • Link Speed
    All of these factors implement, in the end, the speed at which the storage arrays can do their replication tasks.
    Last edited by tomtom1; 04-10-2014 at 08:16 PM.
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  7. VCDX in 2017 Essendon's Avatar
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    #156
    Yep, your RPO and RTO times should be driven by business continuity requirements not by the backups regime. Backups and their frequency should be guided by your business requirements too, not the other way around (like Tom said).

    As for the values, here:

    - RPO = 8 hours
    - RTO = 6 hours
    - WRT = 4 hours
    - MTD = 10 hours (RTO + WRT)
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    #157
    Quote Originally Posted by Essendon View Post

    The amount of time the business can be without their services without incurring significant losses is 6 hours (MTD?). It's been estimated it would take 4 hours for them to recover lost data, recover from backlog and verify operational services (WRT).


    As for the values, here:

    - RPO = 8 hours
    - RTO = 6 hours
    - WRT = 4 hours
    - MTD = 10 hours (RTO + WRT)
    Not 100% sure I agree, but that's why we're on a forum right? Following these numbers, if we say the maximum amount of downtime the business can have their application (MTD) without causing significant issues would be 6 hours, and it would take them 4 hours WRT, then it would mean that there is automatically 2 hours left for RTO.

    Because MTD is the sum of RTO + WRT, and the MTD (6 hours) and the WRT (4 hours) is a given, we should have 2 hours for the RTO.

    So it would still be the total of 6 I came up with, only with WRT and RTO switched. But if you can give me a compelling argument why the 10 hours MTD is correct, I'm all ears!
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  9. VCDX in 2017 Essendon's Avatar
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    #158
    Sure. 6 hours is how long it takes for them to recover their systems (which is the RTO, at this time the servers/VM's/applications/whatever are up and running but no data has been recovered yet) and then it takes them another 4 hours to recover data from backups and verify the data (this'll be the WRT). Then of course, the MTD is the sum of the RTO and WRT, making it 10 hours.

    TBH, I thought exactly the way you provided the answer to the question. But check out the link I've posted about this topic in the VCAP5-DCD resources thread and that should clear things up further.
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    #159
    A technical solution should adhere to business requirements, and not the other way around.
    Wonder if that is always possible though. Business requirements surely include budget as well, and that is where technology sometimes dictates business needs.
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    #160
    Quote Originally Posted by jibbajabba View Post
    Wonder if that is always possible though. Business requirements surely include budget as well, and that is where technology sometimes dictates business needs.
    Then it would be a constraint (in VCAP-DCD terms) and if the budget (constraint) would cause a failure to meet the business requirements, it would be considered a risk. The business would then need to decide to either:

    -> Drop or adjust the business requirement that clashes with the constraint.
    -> Increase the budgetary constraint

    @Essendon: correct?
    Last edited by tomtom1; 04-11-2014 at 06:49 AM.
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    #161
    Ah makes sense. Funny, I did attend the design course back in 4.x days - but that was a glorified sales pitch , if anything .
    My favorite phrase when talking to customers about budget is that every 9 after the comma of uptime, adds a "0" to the price before the comma
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    #162
    I'll come with a more advanced question tomorrow about some common misconceptions (It's 9PM here now)
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    #163
    Question 25:

    Still following the same company we used to, the new admin, Richard, is wondering why Dorothy didn't bring more structure into the organizations vCenter environment. After all, wouldn't it be kinda nice to have the virtual machines grouped by their function, instead of just being a VM in a cluster?

    This is what he came up with:
    Screen Shot 2014-04-12 at 08.04.28.pngScreen Shot 2014-04-12 at 08.04.40.jpg

    OK, nice, in the DR site we have the VM's grouped by their function, which mainly is production. However, the dr-vma virtual machine wasn't really a part of the production, it's more like a management tool, so Richard decided to keep it out of the resource pool for now.

    1) What is the critical misunderstanding that Richard has for grouping virtual machines to create a better overview?
    2) In doing so, what would be the effect in case of CPU contention?
    3) What would be a better way to achieve overview?
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  15. kj0
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    #164
    Quote Originally Posted by tomtom1 View Post
    Question 25:

    Still following the same company we used to, the new admin, Richard, is wondering why Dorothy didn't bring more structure into the organizations vCenter environment. After all, wouldn't it be kinda nice to have the virtual machines grouped by their function, instead of just being a VM in a cluster?

    This is what he came up with:
    Attachment 5188Attachment 5189

    OK, nice, in the DR site we have the VM's grouped by their function, which mainly is production. However, the dr-vma virtual machine wasn't really a part of the production, it's more like a management tool, so Richard decided to keep it out of the resource pool for now.

    1) What is the critical misunderstanding that Richard has for grouping virtual machines to create a better overview?
    Richard has misunderstood what Resource Pools are used for - They aren't used as Folders
    2) In doing so, what would be the effect in case of CPU contention?
    Depending on if Richard has chaged any shares, the Vms will fight for CPU resources. Which can cause lethargic VMs
    3) What would be a better way to achieve overview?
    Under VMs and templates view you can create Folders

    I think thats right.
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    #165
    Correct, but, for question number 2 I'd like a bit more detailed answers (i.e what will happen in times of contentions). The second screenshot posted should give you the information necessary to derive a conclusion.
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  17. kj0
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    #166
    Quote Originally Posted by tomtom1 View Post
    Correct, but, for question number 2 I'd like a bit more detailed answers (i.e what will happen in times of contentions). The second screenshot posted should give you the information necessary to derive a conclusion.
    (I missed the second screenshot. It looks like you have DRS enabled, but will not work due to the resource pool. (I'm missing something, aren't I...)
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    #167
    DRS will work fine with a resource pool. As a matter of fact, you need to have DRS enabled to create a resource pool. What I meant:

    Quote Originally Posted by kj0 View Post
    Depending on if Richard has chaged any shares, the Vms will fight for CPU resources. Which can cause lethargic VMs
    The second screenshot provided you with all the info necessary. Tell me what wil happen if CPU contention were to occur on mini1? How will the resources be divided and what can you learn from the placement of the VM from this?
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  19. kj0
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    #168
    Do you meant that the DR-VMA will take precedence over the Resource pool? I was focusing on the resource pool.


    You don't need DRS for the resource Pool, I've just created one without it. Wouldn't DRS not work for the resource pool as it is connected to a host? It wouldn't move all the VMs under it and because those VMs are tied to that RP.
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    #169
    Quote Originally Posted by kj0 View Post
    Do you meant that the DR-VMA will take precedence over the Resource pool? I was focusing on the resource pool.
    Yes, that would be what I was searching for. The full answer would be: In case of CPU contention, 50% of the available CPU resources go to dr-vma.vcaplab.local, and 50% of the CPU resources go to the production resource pool, which then needs to devide those CPU resources between the 3 virtual machines placed into the resource pool. So you see, placing virtual machines in a resource pool, and some out of the resource pool under the host itself can have tremendous effects on the share.

    Quote Originally Posted by kj0 View Post
    You don't need DRS for the resource Pool, I've just created one without it. Wouldn't DRS not work for the resource pool as it is connected to a host? It wouldn't move all the VMs under it and because those VMs are tied to that RP.
    If you have the situation which I have, in which my host is part of a cluster, you need to have DRS enabled to create a cluster. If you try to disable the DRS functionality after having created a resource pool, you get a nice warning like this.

    Screen Shot 2014-04-12 at 11.26.53.jpg

    When you create a resource pool in a DRS-enabled cluster, the VM's inside that RP are not "bound" to the host. The shares, limits and reservations on the RP itself represent CPU and memory resources in the cluster, not of a specific host anymore. That is why, when you add a host to a cluster, that has a local resource pool, vCenter presents you with the option to graft the resource pools in. You get a message like this:

    Screen Shot 2014-04-12 at 11.38.24.jpg

    I don't know how far along your VCP studies are, but I hope this gives you a basic understanding of how RP integrate with clusters.
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  21. VCDX in 2017 Essendon's Avatar
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    #170
    Question 26

    Richard, our new admin, has decided to persist with the use of resource pools in his cluster. To ensure all VM's are all siblings in the pool, he has dragged dr-vma.vcaplab.local into the Production resource pool. As the number of machines grow in the Production cluster and some contention begins to occur, Richard discovers that the dr-vma machine is getting more shares than other VM's. Why could this be happening, considering he didnt change any values after dragging it into the pool?

    In addition, a System Manager walks up to him one fine day, asking him to reserve all her VM's memory. Now Richard really like this manager and there seems to be something going on between them, so to make her happy he agree to check the "reserve all guest memory" box for her. Overjoyed and starry-eyed the manager walks back to her desk with Richard's eyes following her. Anyways, what are the consequences to Richard's other VM's in the Production cluster. Should he have agreed to her request and what should he have asked her before blindly agreeing to the request?
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  22. kj0
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    #171
    The dr-vma maintains it's previous setting of "High" over the "Low" settings that are already assigned to the Resource Pool.

    Richard should have asked her out on a date before he has to clean up the mess he has created - Now he has no chance with her.

    The VMs (depending on if they have a reservation set prior) would
    A. Not turn on.
    B. Go straight on to the swap file.
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  23. Senior Member tomtom1's Avatar
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    #172
    Nice answer Keiran, but a nice addition would be: He should have investigated whether the VM uses this memory at a constant pace. Whilst I'd stay away from reservations in general if they're not needed, they aren't necessary a bad thing if the resources that are being reserved are actually used. Windows for example has the nasty habit of touching all memory in the boot process. Once the memory is touched, with a reservation, it cannot be used to satisfy needs for other virtual machines anymore.

    Since we can't see the settings of the RP, we can assume that an expandable reservation is enabled (default). This allows the resource pool to steal resources from it's top level resource pool. Even a resource pool with no parent resource pool can steal resources from the host itself, which in fact is one big resource pool.
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  24. VCDX in 2017 Essendon's Avatar
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    #173
    Yep, Windows has that habit of touching all memory when booting while Linux doesn't. On any VMware exam, pay particular attention to the OS of the guest OS when you answer questions involving reservations.

    As for expandable reservation, note that it allows the child resource pool to borrow (or steal, if you like) resources from the parent resource pool to satisfy reservations set on a VM. Read that again - pay attention to "satisfy reservations". It doesn't ask for resources just because a VM suddenly needs more than its reservation. If no VM has a reservation set, "expandable reservation" doesn't do anything.

    So if a resource pool has 6GB RAM available to dish out to its VM's, you can power on one VM with say 4GB RAM but the moment you try to power up another VM with 4GB RAM - you'll be greeted with a nice big red error message saying you cant power on your VM.

    Another thing - continuing the above example, the resource pool wont prevent you creating a VM with say 16GB RAM. You can create whatever you fancy, but it wont let you power it on if you go beyond what's available.
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  25. kj0
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    #174
    Just searching blogs for specific items I feel I need a bit of a better understanding for, and came across this for Resource Pools. Understanding Resource Pools in VMware vSphere | Wahl Network
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    #175
    Great resource there kj0, ensure you lab it up (I'm sure your doing it already) to make it sink in. Some of this stuff doesnt always make sense until you actually do and see it for yourself.
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