User guide

Technical white paper | HP Enterprise Virtual Array Storage and VMware vSphere 4.x and 5.x configuration best practices

Best practice for space reclamation with ESXi 5.0U1 and ESXi 5.1

• Space reclamation in ESXi 5.0U1 and ESXi 5.1 is recommend to be performed during a maintenance window.

Note

The EVA Vdisks are striped across all spindles in the array. Accordingly, putting a host in maintenance mode to carry out the

reclaim operation on inactive ESX datastores (EVA Vdisks) can still have an impact on volumes that are active on other hosts

because all volumes share the same spindle.

Best practice when only 80% of expected capacity is being reclaimed

• Set the Vdisk access mode to write-through and immediately set it back to write-back and retry the reclaim operation.

Finally, it is recommended to run only one instance of VMware block space reclamation operation at a time per EVA array

and per datastore.

UNMAP in ESXi 5.5

In ESXi 5.5, the same considerations discussed above apply. However UNMAP in ESXi 5.5 is performed using the esxcli –

u datastore_uuid –n reclaim_unit instead of the vmkfstools.

Note

The vmkfstools will work with this version of ESX; however, it is deprecated and the syntax is different.

This command reclaims capacity in increments specified by the reclaim_unit. The reclaim_unit defaults to 200 blocks. Thus

on a 1MB datastore, it will attempt to reclaim capacity in 200MB chunks.

By reclaiming capacity in much smaller chunks, ESXi 5.5 is able to effectively address the capacity reservation issue that

previous versions were subject to.

Additionally, ESXi 5.5 always reclaims 100% of the free capacity instead of some arbitrary percentage and only a single

iteration of the command is required to achieve this result. Making ESXi 5.5 space reclamation 100% efficient and effective

compared to previous versions of ESX.

In order to maximize the EVA’s capability to handle UNMAP commands, it is recommended that the following reclaim

increments be used with ESXi 5.5:

• For arrays with FC backend - EVA4400 / EVA8400, the recommended value of reclaim unit is 480.

• For arrays with SAS backend - P63xx / P65xx, the recommended value of reclaim unit is 1280.

Best practice for space reclamation with ESXi 5.5

• Space reclamation in ESXi 5.5 needs to be performed offline.

Best practice for ESXi 5.5 reclaim unit for EVA (assuming 1MB block size)

• Use reclaim unit of 480 for EVA4400/EVA8400.

• Use reclaim unit of 1280 for P63xx/P65xx.

Table 13 provides an overview of key differences between the operation of UNMAP in the versions that support UNMAP.