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FusionCloud 6.3.0 Solution Description 05

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Local Disk

Local Disk

Definition

A local disk is a disk attached to the physical machine (host) where an instance resides, and is a temporary block storage device. Storage devices of this type provide block-level data access capability for instances, and present high I/O performance, low latency, and high throughput. Local disks are temporary block storage where data cannot be stored permanently. When your instance is migrated from one host machine to another, the local disk will not be migrated with the instance, and data will be lost. EVS disks can be used for permanent storage. Data in EVS disks is not lost with the start, stop, or migration of the instance.

Table 7-2 shows the differences between local disks and EVS disks.

Table 7-2 Differences between local disks and EVS disks

Type

Difference

Application Scenario

Local disk

Compared with EVS disks, local disks have a more stable I/O performance and higher throughput, but do not support live VM migration or flavor modification. The capacity and number of local disks are not limited by VDC quotas, and their usage statistics cannot be collected.

The performance of local disks varies with the load on the physical host and single point of failure (SPOF) may be involved. Therefore, local disks are suitable for systems that run for a short period of time with a relatively low requirement on stability and reliability.

It is recommended that you use data redundancy at the application layer, synchronizing or backing up critical data on local disks to other instances or EVS disks, respectively, to ensure data availability.

EVS disk

EVS disks feature high reliability and storage performance and support live migration and disk upgrade and degrade. The capacity and number of EVS disks are limited by VDC quotas, and their usage statistics can be collected.

If your service applications run on long-term systems that have relatively high requirements on stability and reliability, it is recommended that you use EVS disks.

Typical deployment scenarios of FusionCloud 6.X are Region Type I, Region Type II, and Region Type III. Table 7-3 shows the relationship between disks used by ECSs and local disks and EVS disks in Region Type I, Region Type II, and Region Type III.

  • Life cycle: The life cycle of local disks depends on the life cycle of ECSs. Therefore, the life cycle of local disks starts or ends as the life cycle of ECSs starts or ends.
  • Configuration selection: Local disks can only be started when ECSs are started. Therefore, when a local disk is a system disk, it can only be used as the boot device when the ECS flavor is created. When a local disk is a data disk, it can only be used as a temporary disk when the ECS flavor is created. .
Table 7-3 Relationship between disks for ECSs and local disks and EVS disks in different deployment scenarios

Deployment Scenario

System Disk for ECS

Data Disk for ECS

Region Type I

Only EVS disks can be used as system disks.

Only EVS disks can be used as data disks.

Region Type II

Local disks or EVS disks can be used as system disks.

Local disks or EVS disks can be used as data disks.

Region TYpe III

Local disks or EVS disks can be used as system disks.

Local disks or EVS disks can be used as data disks.

Impact on the data status of local disks when you perform operations on instances

Table 7-4 shows the impact on the data status of local disks when you perform operations on the instances where the local disks reside.

Table 7-4 Impact on the data status of local disks when you perform operations on the instances where the local disks reside

Operation on an Instance

Data Status of a Local Disk

Impact

Restarting an OS/Restarting an ECS

Retained

The local disk is retained, and data is retained.

Stopping an OS/Stopping an ECS

Retained

The local disk is retained, and data is retained.

Releasing an ECS (deleting an instance)

Erased

The local disk is erased, and data is not retained.

Stopping the device and migrating data

Erased

The local disk is erased, and data is not retained.

Application Restrictions

If you create an instance configured with a local disk and the local disk serves as the system disk, you do not need to manually initialize the local disk, and the local disk will be automatically initialized after the instance is created. If the local disk serves as a data disk, you need to log in to the instance, and then partition and format the local disk. In addition, you cannot perform certain operations on local disks as you do on EVS disks:

  • No blank local disks can be created independently, and no local disks can be created from snapshots.
  • Local disks cannot be attached on the console.
  • Local disks cannot be independently detached and released.
  • The capacity of local disks cannot be expanded.
  • Local disks cannot be reinitialized.
  • No snapshots can be created for local disks, and therefore, local disks cannot be rolled back from snapshots.
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Updated: 2019-04-23

Document ID: EDOC1100026685

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