Veeam Support Knowledge Base
Slow Restore Performance With Direct SAN Mode

Slow Restore Performance With Direct SAN Mode

KB ID:	2052
Product:	Veeam Backup & Replication
Published:	2015-07-08
Last Modified:	2022-11-11

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Challenge

When performing a Full VM Restore or Virtual Disk Restore using Direct SAN Restore, the performance may be sub-optimal when the restored Disk Type Setting is set to Thick (lazy zeroed).

Cause

When using Direct SAN to restore a disk with it's disk type set to Thick (lazy zeroed), overall restore performance can be affected because of repeated disk manager API calls to ClearLazyZero and AllocateBlock.

Solution

Option 1: Use 'Thick (eager zeroed)' Disk Type

When restoring via Direct SAN, disks must be restored as Thick, either lazy zeroed or eager zeroed. Performance has been shown to be much higher when using the eager zeroed option¹.

Entire VM Restore

On the Datastore tab of the Full VM Restore wizard, use the Disk Type button in the bottom-right corner to set the restored disk type to "Thick (eager zeroed)."

Virtual Disk Restore

On the Disk Mapping tab of the Virtual Disk Restore wizard, use the Restored disk type dropdown box to select "Thick (eager zeroed)."

Option 2: Use Network or Virtual Appliance Transport Mode

If you'd prefer to restore the disk as Thick (lazy zeroed), performance can be improved by using the "Picky proxy to use" option in the Full VM Restore and Virtual Disk Restore wizards to select either a proxy that does not have Direct SAN capability or a proxy that has been manually configured to use either Virtual Appliance or Network transport mode.

Additionally, simply selecting the disk type Thin will force the restore to use any other transport mode because Direct SAN cannot restore disks as Thin provisioned.

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