Introduction to Cloud Server Local Storage ("Disks") and Disk Speeds

Description

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Provides a complete overview of how local storage attached to Cloud Servers operates, including an explanation of the Disk Speed feature which provides users with the ability to apply different levels of disk performance to local Cloud Disks.

Introduction to Cloud Server Local Storage

CloudControl supports local storage via storage volumes (i.e. "disks") that are attached to a variety of virtual controllers which emulate a specific hardware type. Most Images and Servers use SCSI controllers for this purpose, but the system also supports IDE and SATA controllers as well as read-only files on CD-ROM and Floppy devices. Being a virtualized environment, each storage volume ("disk") is delivered via a VMDK file that's deployed to a LUN on the underlying storage infrastructure. Each disk is assigned a "disk speed" which determines the performance characteristics of the underlying storage that will be used for that specific local storage volume. Local disks using the same disk speed may or may not be deployed to different physical LUN's on the storage infrastructure. ISO and FLP files do not have disk speeds and are always on the Standard disk speed.

From the Operating System, each local disk appears to be an external hard disk attached to a specific spot on the controller. When a Cloud Server is deployed, it will inherit the same virtual controllers, disk sizes, and disk locations as the Source Image. However, users can choose to modify the speed of a disk on a deployed Server to be different than that which was used when the Image was created. For details, see the instructions on how to deploy Servers at How to Deploy a Cloud Server from a Guest OS Customization Image and How to Deploy a Cloud Server from a Non-Guest OS Customization Image

Note: Client Images always use Standard Storage and are always billed as Standard Storage. Client Images have “disk speed" information associated with each disk, but these speeds are simply metadata that the system defaults to when you deploy a server from that Image. The Images themselves are actually stored on Standard storage. Since the system "defaults" to the disk speed of the Source Image, users can also modify the default disk speeds associated with a Client Image as described in How to Manage a Client Image.

Note: Most Server BIOS are programmed to boot the Operating System from SCSI Controller 0, Position 0, but users can modify the BIOS through the Console to change this behavior. 

Virtual SCSI Controllers and Adapters

The system supports up to four virtual SCSI controllers per Cloud Server. Each SCSI controller uses a specific "adapter" that defines how the SCSI controller is perceived by the guest Operating System. There are four adapters supported by vSphere:

  • BusLogic Parallel - This was one of the first two emulated vSCSI controllers made available on the VMware platform, and remains commonly used on older versions of Windows as the driver is available by default.
  • LSI Logic ParallelThis was the other emulated vSCSI controller made available on the VMware platform and remains commonly used on UNIX Operating Systems 
  • LSI Logic SAS - This is a newer evolution of the parallel driver supported (and in some cases required) for newer versions of Microsoft Windows. It was designed to replace the BusLogic Parallel adapter and provides better performance than the original BusLogic Parallel adapter.
  • VMware Paravirtual - This is a VMware-specific driver that is virtualization-aware and designed to support very high throughput with minimal processing cost and is, therefore, the most efficient driver. However, this driver requires that VM Tools be installed and running in order to function properly. There are some other restrictions, particularly on older operating systems - review the appropriate VMware documentation for more details. 
  • More details on each of the adapters described above are available the VMware Blog article Which vSCSI controller should I choose for performance?

Note that although there are four adapters supported, VMware does not support all of them on every Operating System. When adding a Controller, the system will only make available adapters approved for the Server's Operating System. The Supported Operating Systems dashboard will help you identify what adapters are "available" and which one is "recommended" by VMware for a given operating system as described in Navigating the Supported Operating Systems Dashboard

Each SCSI controller provides 15 "positions" in which a local storage "disk" can be attached. These positions are numbered from 0 through 15, with the 7 position reserved as it is used by the virtual SCSI adapter. This means that with the full complement of four SCSI controllers, there are 60 potential positions where local disks can be placed.

Users can add or remove SCSI controllers for a Cloud Server as described in:

Virtual SATA Controllers

The system supports up to four virtual SATA controllers per Cloud Server. All SATA controllers emulate a standard AHCI 1.0 Serial ATA Controller (Broadcom HT 1000) - there are no separate adapters as there are with SCSI controllers. As described in VMware SCSI Controller Options, use of SATA controllers is not recommended for high I/O environments.

Each SATA controller provides 30 "positions" in which either a local storage "disk" or a CD-ROM device can be attached. These positions are numbered from 0 through 29. This means that with the full complement of four SATA controllers, there are 120 potential positions where either local disks or CD-ROM devices can be placed.

SATA controllers are supported only if already present on Images or Servers, you cannot add or remove SATA controllers on an existing Cloud Server. Therefore, if you wish to use SATA, you will need to import a Client Image with the desired number of SATA controllers already present. SATA is not supported on all Operating Systems. Check the VMware Compatibility Guide for more details.

Virtual IDE Controllers

The system supports up to two virtual IDE controllers per Cloud Server. All IDE controllers emulate a standard Intel 82371AB/EB PCI Bus Master IDE controller - there are no separate adapters as there are with SCSI controllers.

Each IDE controller provides only two "positions" in which either a local storage "disk" or a CD-ROM device can be attached - slots 0 and 1. IDE works under a Master/Slave configuration, so the "1" position can be used only if either a "disk" or CD-ROM device is in the "0" position of the same controller. Therefore, the system will prevent deletion of a local disk in position 0 if there is a local disk in position 1.

VMware's import process inserts IDE controllers on all images imported through the OVF process, so the controllers are present on almost all Images and Cloud Servers. The system does not support addition or removal of IDE controllers.

NOTE: IDE Controllers do not support "expanding" a disk and require the server to be powered off in order to add a disk to the controller.

CD-ROM Devices

CD-ROM devices may be present on IDE or SATA controllers only if already present on Images or Servers, you cannot add or remove the CD-ROM devices from the controller. Therefore, if you are looking to use a CD-ROM device as described below, you will need to import a Client Image with the desired CD-ROM devices and/or ISO files already present.

CD-ROM devices may have an ISO file attached, in which case they provide read-only access to the ISO file through the virtual CD-ROM device. Otherwise, the CD-ROM device does not provide any use. All such ISO files are placed on Standard Disk Speed (see below for details) and billed based on their file size as if they were a local disk on Standard disk speed. A server or image can have as many CD-ROM devices and ISO files as supported by the controllers, but the total combined size of all ISO and FLP (see below) on a Cloud Server/Image cannot exceed the Maximum Disk Size (GB) for the data center location.

Currently, the system allows ISO only if it is already present on the Image or Server, so they need to be included on an Imported Image. ISO files may be permanently removed from a Cloud Server, but they cannot be added, modified, or replaced. You will have to import a new Image if you want to make changes. 

Floppy Controllers

The system does support up to two Floppy Controllers that can have an FLP file attached, in which case they provide read-only access to the FLP file through the virtual floppy device in the same manner as ISO support. The system allows Floppy and associated FLP files only if it already present on the Image or Server, so they need to be included on an Imported Image. FLP files may be permanently removed from a Cloud Server, but they cannot be added, modified, or replaced. You will have to import a new Image if you want to make changes.

Disk Minimums and Maximums 

Beyond that, there are four sets of limits associated with local storage on a Cloud Server, each of which varies by User-Manageable Cluster or Data Center location and can be identified as described in How do I Identify Hardware Specifications and Capabilities Available in a Data Center Location:

  1. The size of each individual disk must fall within a specified range of Minimum Disk Size and Maximum Disk Size
  2. The total number of disks must fall within the range dictated by the data center location's Minimum Disk Count and Maximum Disk Count
  3. Maximum Total Storage defines the maximum aggregate amount of "local" storage associated with a Cloud Server
  4. There is a smaller Maximum Total Storage for an Image limit on the total size of the Cloud Server if it can be cloned to create a Client Image.

Effective March 23, 2017,  the following 'default' limits are set in most (but not all) Public Cloud locations. Private Cloud locations are less likely to follow these default values. We are providing this list for convenience but we recommend reviewing the specifics of the location for as described in How do I Identify Hardware Specifications and Capabilities Available in a Data Center Location for a more accurate answer.

PropertyMCP 2.0 Default SettingMCP 1.0 Default Setting
Maximum Total Storage for Cloud Server (GB)30,00011,000
Maximum Total Storage for Client Image (GB)3,0002,600
Minimum Disk Size (GB)110
Maximum Disk Size (GB)10001000
Minimum Disk Count11
Maximum Disk Count6015

When disks are added to a Cloud Server, they will appear as unformatted drives that need to be formatted for use. A User can choose a specific controller and position on which to install the drive or have the system insert the drive in the "next available" SCSI position. For additional details on how to add a disk, see:

These disks can also be removed from the Cloud Server as described in:

Any individual disk attached to a deployed Cloud Server can be increased in size should greater capacity be required – though note that like a newly-added disk, the additional storage is delivered as an unformatted increase in the size of the volume and therefore needs to be formatted by the OS for use. For more details, see:

Introduction to Disk Speeds (Tiered Storage)

Local storage ("disks") each have a specific "disk speed" that defines the performance characteristics associated with the local storage. CloudControl will allow you to decide which performance characteristic a given Cloud Server disk should utilize based on the disk speed. Each local storage volume is treated independently in terms of its performance. Disk speeds allow the user to select a level of performance that is focused on the intended function of the disk. For example, log file storage might require a lower level of performance while database files may require a faster level of performance. Because the disk speed can be set at an individual disk level, a given Cloud Server can have different disk speeds depending on how they plan to use the disks. Different disk speeds are available in a given data center location.

There are two types of available disk speeds. More details are provided in the below sections but the overview is:

  1. Variable IOPS Disk Speeds (Provisioned IOPS) allow users to choose the IOPS and corresponding throughput for a given disk. There are some limitations on the IOPS based on the size of the disk, but these speeds will allow a wide range of possible performance values. Users can also change these performance values even after they're set. IOPS and Throughput are universally enforced with these speeds.
  2. Fixed IOPS Disk Speeds (Standard, High Performance, Economy, SSD) provide IOPS and corresponding throughput based either on the size of the disk or the underlying storage infrastructure. When IOPS and Throughput are enforced, larger sized disks will receive correspondingly higher IOPS based on a fixed ratio of IOPS and Throughput per GB. See the Fixed IOPS Disk Speeds section later in the article for more details as to how these speeds work in a given location.

The "disk speed" associated with each Server is visible in the Manage Server dialog of the Admin UI in a row that is shown underneath the associated Controller with the position and size of the individual disk:

 

The "disk speed" of a given disk can be changed at any time to any of the disk speeds available in a given location/cluster. For more details, see:

Understanding IOPS and Throughput Performance


IOPS and Throughput Enforcement Not Always Enforced for Fixed IOPS Disk Speeds

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The following section describes how CloudControl enforces IOPS and Throughput performance.

The enforcement methodology described in this section always applies to Provisioned IOPS disk speed. This section does not always apply to Fixed IOPS disk speeds. See the Fixed IOPS Disk Speed Definition Enforcement Matrix later in the article for details on where the methodology applies.

Real-world storage performance is governed by a multitude of factors, including application and OS variables, storage latency, and other factors. However, at a high level, one of the key factors is Disk Throughput, where:

  • Disk Throughput = IOPS (Inputs/Outputs per second) x Block Size

In the context of CloudControl, the system provisions disk speed performance characteristics based on IOPS, assumes a 16 KB block size, and sets a corresponding Disk Throughput limit based on the IOPS and 16 KB block size. The result is that the disk is governed by both an IOPS limit and a Disk Throughput limit where the Throughput limit is equal to IOPS x 16 KB. The net effect is that only one limiter is likely to establish the maximum performance at any given time. If the block size is less than 16 KB, IOPS will be the limiting factor and corresponding Disk Throughput will be less than the maximum Disk Throughout allowed. If the block size is greater than 16 KB, Throughput will be the limiting factor and the corresponding IOPS will be less than the maximum IOPS allowed.

  • Example: User sets up a Provisioned IOPS disk of 100 GB with 1,000 IOPS. CloudControl will provision the disk with a limit of 1000 IOPS and a Disk Throughput limit of 16,000 KB/second (1000 IOPS x 16 KB)
    • If 16 KB Block Size is consistently used, the maximums are in perfect alignment. 1,000 IOPS (IOPS limit) x 16 KB block size = 16,000 KB/second (same as disk throughput limit)
    • If an 8 KB Block Size is consistently used, 1,000 IOPS (maximum IOPS limit) x 8 KB block size = Disk Throughput 8,000 KB/second. So overall Disk Throughput matches the expected value given the IOPS and KB block size, but this provides less Throughput than the theoretical maximum.
    • If a 32 KB Block Size is consistently used, then at 500 IOPS, 500 IOPS x 32 KB block size = 16,000 KB/second (maximum Throughput value). Since overall Disk Throughput has hit the maximum, only 500 IOPS can be achieved.

As noted, in real-world applications, the block sizes often vary and other OS and application variables will have an effect on actual performance. Therefore, the IOPS and Throughput settings represent maximum IOPS and Throughput performance in locations and disk speeds where these values are enforced. Users can expect consistent performance approaching these maximum settings based on the IOPS value assigned to a given disk.

Variable IOPS Disk Speeds (Provisioned IOPS)

Provisioned IOPS is currently the only disk speed that falls into this category. With this category of disk speeds, users can choose the IOPS/Throughput performance for each disk by selecting a given IOPS value for the disk. The IOPS value must conform to a set of rules established for the disk speed in the data center location. The rules for the Provisioned IOPS disk speed are the same in all Public Cloud locations where the speed is available but may vary in Private Cloud locations. The Public Cloud location values are listed below in parenthesis but you can identify the specific characteristics of any location as described in How do I Identify Hardware Specifications and Capabilities Available in a Data Center Location.

  • Min IOPS Per GB (3 IOPS/GB) - When setting the IOPS value, you must provision a minimum of 3 IOPS per GB based on the size of the disk. So if the disk is 100 GB in size and using Provisioned IOPS, you must assign at least 300 IOPS.
  • Max IOPS Per GB (15 IOPS/GB) - When setting the IOPS value, you can provision a maximum of 15 IOPS per GB based on the size of the disk. So if the disk is 100 GB in size and using Provisioned IOPS, you cannot assign more than 1,500 IOPS to the disk unless you expand the size.
  • Min Total IOPS (16 IOPS) - This is the minimum IOPS value that can be assigned to any disk. This limit does not come into play much in Public Cloud locations except that you cannot use Provisioned IOPS with a disk size of 1 GB as even that the Max IOPS per GB setting of 15 GB does not reach the Minimum IOPS limit of 16.
  • Max Total IOPS (15,000 IOPS) - This is the maximum IOPS value that can be assigned to any disk. In Public Cloud locations, this limit does not come into play but in locations where disk sizes of greater than 1,000 GB are allowed, it means you may not be able to provision the full 15 IOPS/GB maximum with large size disks.

You don't need to memorize these rules, as when setting IOPS values for a Variable IOPS disk, the UI will present a slider with the available IOPS values based on the location's setting and the current disk size:

 

Once a disk is assigned a Provisioned IOPS disk speed, you can modify the IOPS at any time as described in How to Manage Storage on a Cloud Server. However, note that you cannot expand the size of the disk and modify the IOPS value at the same time. In scenarios where a user is trying to drastically expand the size of a small disk, users may need to expand the disk size and modify the IOPS value in steps to stay within the Min/Max rules.

  • Example: Suppose you have a 100 GB Provisioned IOPS disk with 1,000 IOPS and you want to expand that disk to 1,000 GB in size. The Maximum IOPS for a 100 GB Provisioned IOPS disk is 1,500 IOPS (15 IOPS/GB). The minimum IOPS for a 1,000 GB Provisioned IOPS disk is 3,000 IOPS (3 IOPS/GB). Therefore, the system will not allow you to expand the 100 GB directly to 1,000 GB. If you set the IOPS of the 100 GB disk to the 1,500 IOPS maximum, you can expand the size to 500 GB (maximum size given 3 IOPS/GB minimum and 1,500 IOPS). You can then modify the IOPS of the now 500 GB disk to anything between 3,000 IOPS (minimum IOPS needed for a 1,000 GB disk) and 7,500 IOPS (maximum given 15 IOPS/GB). The system will now allow you to expand to 1,000 GB in size, after which you can set the IOPS to anything within the 3,000 IOPS minimum and 15,000 IOPS maximum for a disk this size.

Note that in the current CloudControl release, there are also two limitations on the use of the new Provisioned IOPS disk speed

  1. Users can only change the disk speed of an already provisioned disk to a Provisioned IOPS disk speed as described in How to Manage Storage on a Cloud Server. This means:
    1. You cannot directly add a disk with a Variable IOPS disk speed. Instead, you must first add the disk with a Fixed IOPS disk speed, and then change the disk speed as described in How to Manage Storage on a Cloud Server.
    2. You cannot deploy a Cloud Server with any disk assigned a Variable IOPS disk speed. Instead, you must provision all disks with a Fixed IOPS disk speed, and then change the disks you want to use the Provisioned IOPS disk speed as described in How to Manage Storage on a Cloud Server.
  2. Customer Image disk speed metadata does not support Variable IOPS disk speed. If you clone a Server with Provisioned IOPS disk speeds to create a Customer Image, all disks with Provisioned IOPS will be set up with the disk speed metadata set to the Standard disk speed. You will also not be able to set Image disk metadata to Provisioned IOPS as described in How to Manage a Client Image.

Both of the above limitations will be removed in a future release.

Fixed IOPS Disk Speeds (Standard, High Performance, Economy, SSD)


Fixed IOPS Disk Speeds Vary By Location

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Fixed IOPS Disk speeds currently perform differently depending on the location. See the Fixed IOPS Disk Speed Definition Enforcement Matrix section below for specifics as to which of the two methods described below apply to a given location.

Fixed IOPS Disk Speed Definition where IOPS is NOT Enforced

In Fixed IOPS Disk Speed definition where IOPS is not enforced, performance characteristics are primarily based on the underlying disk storage infrastructure supporting the disk speed. In Public Cloud locations, the following infrastructure is used:

  • Standard - Cloud disks deployed as Standard speed are deployed on LUN's powered by a Hybrid Disk configuration consisting of 2 TB 7200 RPM Nearline SAS disks in a RAID5 configuration that is fronted by an extensive "Fast Cache" Solid-State Disk infrastructure. 
  • High Performance - Cloud disks deployed as High Performance speed are deployed on LUN's powered by a Hybrid Disk configuration consisting of 600 GB 15000 RPM Nearline SAS disks in a RAID5 configuration that is fronted by an extensive "Fast Cache" Solid-State Disk infrastructure.
  • Economy - Cloud disks deployed as High Performance speed are deployed on LUN's powered by a disk configuration consisting of 3 TB 7200 RPM Nearline SAS disks in a RAID5 configuration. There is NO "Fast Cache" fronting for this storage level.

Note that since there are no IOPS or Throughput controls enforced in this scenario, there may be inconsistent performance levels between disks deployed on the same disk speed, even when deployed in the same data center location. To increase IOPS performance for a given volume, users can upgrade to a higher-performing disk speed. In some cases, expanding the size may also improve performance.

Fixed IOPS Disk Speed Definition where IOPS is Enforced

With Fixed IOPS disk speeds (Standard, High Performance Economy, SSD), the system will use a fixed IOPS/GB ratio to determine the IOPS and Throughput enforcement for a given disk as described in the Understanding IOPS and Throughput Performance section above. The speeds are enforced in Public Cloud locations are according to the following table:

Disk SpeedMaximum IOPS per GB

Throughput per GB

Standard116 KB
High Performance348 KB
Economy0.34.8 KB
  • Example: User sets up a 100 GB disk. Using fixed IOPS disk speeds, the corresponding performance limits would be:
    • 100 GB Standard Disk = 100 IOPS and 1,600 KB/second throughput
    • 100 GB High Performance Disk = 300 IOPS and 4,800 KB/second throughput
    • 100 GB Economy Disk = 30 IOPS and 480 KB/second throughput

In locations that are using this enforcement method, Fixed IOPS disks will operate with consistent maximum performance given the same disk size and speed. Behavior will mimic the Provisioned IOPS disk speed except that the IOPS and Throughput settings are fixed based on the size of the disk. To increase IOPS performance for a given volume, users can either increase the size of the volume or upgrade to a higher-performing disk speed. 

Fixed IOPS Disk Speed Definition Enforcement Matrix

COMING SOON - currently, users can assume IOPS and Throughput is not enforced for any Fixed IOPS Disk Speed (Standard, High Performance, Economy, SSD).

Availability and Use of Different Disk Speeds

The availability of specific Disk Speeds is configured for each Data Center and User-Manageable Cluster. (User-Manageable Clusters are available in certain Private Cloud and Hosted Private Cloud Data Center locations. For more information about User-Manageable Clusters, see Introduction to User-Manageable Clusters.) As such, not all User-Manageable Clusters and Data Center locations have the same "disk speed" infrastructure available. Only the "Standard" disk speed is available in all Clusters and Data Centers. To identify what speeds are available in a given Cluster or Data Center, view the summary information as described in How do I Identify Hardware Specifications and Capabilities Available in a Data Center Location

It is possible, although unusual, for a disk speed to exist but not currently be available for use on new disks added to a Server. You can identify this condition (and the reason why it's no longer available) through the "Disk Speeds Available" field when viewing a Data Center's capabilities as described in How do I Identify Hardware Specifications and Capabilities Available in a Data Center Location.

How to Use Multiple Disk Speeds

There are two ways to set the disk speed for a Cloud Server:

  • You can choose the specific speed of each disk when a Server is deployed. By default, the Admin UI will present the "default" disk speeds associated with an OS or Client Image. You can modify these "default" speeds through a dialog on the Server as described in:
  • Client Images inherit the "default speed" of each disk based on the speed of the disks on the Cloud Server when the Image was created. You can edit the "default speed" of each disk associated with a Client Image as described in:
    • How to Manage a Client Image
    • Note the Client Images lose any disk speed characteristics when a Client Image is exported, as the OVF format does not support disk speed information. This means that all Imported Images will initially have all disk speeds set to Standard.
  • Once a Server is deployed, you can manage the performance characteristics an individual disk as described in:

Reporting and Billing for Different Disk Speeds 

Each disk speed is reported and tracked separately from a usage perspective. For Variable IOPS disk speeds, two usage elements are calculated: one based on the IOPS assigned to each disk using the speed and another based the size of each disk using the speed. Fixed IOPS disk speeds are calculated with a single usage element solely based on the size of the disk. For more details, see Introduction to Usage Reporting.

From a reporting perspective, the system provides reporting for each disk speed's element:

  • The Summary Usage Report provides a daily location-level summary on the aggregate storage usage of all Cloud Servers in a Geographic Region. For details, see How to Create a Summary Usage Report
  • The Detailed Usage Report provides a daily asset-level report how storage usage was calculated for each Cloud Servers in a Geographic Region. For details, see How to Create a Detailed Usage Report

Each different "disk speed" will be charged at its own rate. Refer to your Cloud Provider's rate card for more information on the specific rates for each disk speed a given data center location.

 

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