Using a Shared EVS Disk

A shared EVS disk can be attached to a maximum of 16 cloud servers and allows concurrent reads/writes from these servers.

You must set up a distributed file system or cluster management system when using shared EVS disks, or concurrent access will fail and data may be lost.

You are advised to use sharing together with SCSI and attach the shared SCSI disk to ECSs in the same anti-affinity ECS group. Shared SCSI disks support SCSI reservations.

What are anti-affinity and SCSI reservations?

Anti-affinity policy of ECS groups: ECSs in such a group will be created on different physical host for improved reliability.

SCSI reservation mechanism: If an ECS sends a SCSI reservation command to a shared EVS disk, the disk will be displayed as locked to other ECSs to prevent simultaneous reads/writes to this disk from multiple ECSs.

ECS groups and SCSI reservations have the following relationship: SCSI reservation on a single EVS disk cannot differentiate multiple ECSs on the same physical host. For that reason, if multiple ECSs are running on the same physical host, SCSI reservation will not work properly.

Parent Topic: EVS Usage Guidelines

Previous topic: Purchasing and Using an EVS Disk

Next topic: Expanding Capacity of an EVS Disk

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