Equipos de DRX y ajustes operarios

Managing the provisioning capacity of each provisioning group’s reservations so that machine requests never fail due to lack of capacity is an important task of Enterprise Administrators.

Managing Virtual Reservation Capacity and Overreservation

vCAC uses five terms when displaying information about virtual resource usage:

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physical — Actual memory or storage capacity of a virtualization compute resource.

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reserved — Specified machine quota, memory, or storage of a vCAC reservation, or of the total of vCAC reservations on a compute resource.

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allocated — Amount of a resource assigned to provisioned machines.

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used — Amount of storage actually in use by provisioned machines.

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free — all unused physical capacity on a storage path.

When a virtual reservation’s specified machine quota, memory, or storage is entirely allocated, no more machines can be provisioned from it. Because allocated memory and storage are not always the same as used memory and storage, however, this allocation limit may result in using less than the available physical capacity of a compute resource. For this reason, there are two situations in which it is appropri- ate for Enterprise Administrators to overreserve a compute resource—that is, to create virtual reserva- tions on the compute resource that total more than its physical capacity for memory, storage or both.

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Since memory usage by virtual machines varies from moment to moment depending on whether and how they are used, the average and peak usage for a group of machines may be

Virtualization compute resource

Storage

Type Storage Configuration Thin provisioning is used …

ESX Server NFS --- always

local, iSCSI ---

when VirtualMachine.Admin.ThinProvision=True Hyper-V Server --- ---

XenServer --- thin provisioning always standard provisioning never

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significantly less than the memory allocated (which was specified in the blueprint with peak rather than continuous requirements in mind).

For example, if a reservation has 8 GB of memory and there are 4 powered-on machines with 2 GB of memory each provisioned on it, the reservation’s memory is fully allocated and no more machines can be provisioned. But if the peak total memory usage of these machines never exceeds 4 GB, 4 GB of compute resource memory is never in use but at the same time unavail- able for provisioning more machines. If there are four such reservations on a compute resource with 32 GB of physical memory, no more machines can be provisioned on the compute resource but 16 of its 32 GB of memory are not in use.

In this case, the Enterprise Administrator might assign 16 GB of memory to each reservation for a total of 64 GB; the compute resource would then be overreserved, with the Memory Reserved (%) column on the compute resources page showing 200%, but actual memory usage would be within the physical capacity of the compute resource.

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As noted in the previous section, for virtual reservations on standard storage allocated and used storage statistics are the same, but when machines are provisioned using a space-efficient tech- nology, a reservation’s storage used can be significantly less than its storage allocated. When this is the case, the difference can be calculated by comparing the allocated and used storage figures shown in the StorageAllocated % and StorageUsed columns on the Reservations page and the Storage Allocated and Storage Used columns on the compute resource page. If some or all of a compute resource’s storage is space-efficient, storage used is likely to consis- tently be significantly less than storage allocated, which results in the allocation limit preventing the use of the unused storage. For example, a compute resource with 300 GB of physical stor- age might typically show 250 GB allocated but only 125 GB used. In such a case, the Enterprise Administrator might increase the storage reserved on the compute resource to 500 to make more available for allocation, overreserving it at 167% (low enough to avoid using 100% of the physical storage).

Managing Cloud Reservation Capacity

Because of the potential expense of cloud machines, you should consider carefully before creating a cloud reservation with an unlimited machine quota.

Managing Physical Reservation Capacity

Assessing allocation of physical reservations is a relatively straightforward matter. There are three num- bers to be compared:

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Total number of machines in the reservation

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Machine quota of the reservation, which is a limit on the number of machines that can be man- aged at one time

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Number of machines that are actually provisioned, or allocated

Note: Unlike virtual machines, powered-off physical machines are included in all allo- cation statistics.

The machine quota of a physical reservation does not have to be different from the total number of machines, but you may want to make the former less than the latter simply to hold some number of machines in reserve. (If you do not specify a quota, the effective machine quota will always be the num-

ber of machines in the reservation.) The Reservations page compares allocation to quota for each listed reservation.

You can also review the amount of a provisioning group’s total reserved physical quota that is currently allocated on the Provisioning Groups page.

Reservation Alerts

Reservation alerts enable an enterprise administrator to alert users when thresholds on reservations are reached so the user can track capacity usage. Thresholds can be set as a percentage of the total com- pute resources available. When a threshold is exceeded, an email is sent to a designated person or to a set of people. The enterprise administrator can adjust the frequency at which alerts are sent as well as receive copies of all email alerts. Alerts can be created for the following:

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Physical resources of a reservation including memory, CPU, and storage

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Total number of machines allocated against the reservation

Note: If the reminder is blank, you will receive the alert only once. Otherwise, you will receive an email at the frequency you have established.

Reservations are checked daily by running a scheduled workflow. The workflow collects any alerts for all existing reservations. If there is at least one alert set up, the workflow collects data on the following:

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Current capacities (adding the capacities of each machines to get the vCPUs used)

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Allocated capacities

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Limits for each capacity

For each defined alert, the workflow compares the allocated amount against the prescribed limit. All capacities that are over the prescribed limit are summarized in an email that is sent (asynchronously) to the specified set of recipients.

Reducing Reservation Usage by Attrition

You may at times want to reduce the number of machines on a particular reservation over the long term while keeping the reservation and the existing machines on it active. You can do this by reducing the reserved memory or storage of a virtual reservation or the machine quota of a virtual, cloud or physical reservation below the amount currently allocated. This allows management of existing machines to con- tinue without change while preventing provisioning of new machines until allocation falls below the new reserved amount.

For example, suppose a provisioning group has a physical reservation containing 20 provisioned machines expiring over the next 90 days, and you want to reduce it by attrition (as the existing machines expire and are decommissioned) to no more than 15 machines. Simply set the machine quota to 15. No further machines can be provisioned, regardless of how many unprovisioned machines are included in the reservation, until the number of provisioned machines falls to 14 or below.

Note: Because virtual machines that are powered off are not included in allocated memory and machine quota totals, reducing the memory or machine quota of a virtual reservation below the amount allocated prevents powered-off machines from being powered on, as well as preventing provisioning of new machines.

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