Slow copy performance with 'cp' between datastores

[Gabriel Onay]

I noticed that the copy of a vmdk file is very slow between 2 datastores with the command 'cp' on an ESXi. The datastore browser does it much faster.

So I've tested the following:

For my test i used a 5 GB vmdk-file (thick).

Copy from Datastore1 to Datastore2:

     with 'cp': time ~ 4:04 minutes

     with FastSCP: time ~ 2:55 minutes

     with Datastore Browser: ~ 36 seconds

     with vmkfstools -i: ~ 35 seconds

Did anyone know why this is so or have observed the same?

Regards

OVE

[piaroa]

Yup, cp has always been slower than vmkfstools, and I think that it's frowned upon as a method for copying vmdks.

[Gabriel Onay]

Hi

I think the Datastore Browser used vmkfstools. That would explain the same copy time.

[Gabriel Onay]

I made the following discovery:

I tested with on vmdk-file with following parameters:

     vmdk-file (thin): size 3,36 GB of 20 GB,

     Guest OS shows 2,6 GB

Copy time from Datastore1 to Datastore2 with Datastore Browser: ~ 24 secounds

I maked an 1 GB testfile in the guest-vm. After this step the vmdk-file has this parameters

     vmdk-file (thin): size 5,35 GB of 20 GB,

     Guest OS shows 3,6 GB

Copy time from Datastore1 to Datastore2 with Datastore Browser: ~ 35 secounds

After i deleted the testfile:

     vmdk-file (thin): size 5,35 GB of 20 GB,

     Guest OS shows 2,7 GB

Copy time from Datastore1 to Datastore2 with Datastore Browser: ~ 35 secounds

I converted the vmdk-file in thick:

     vmdk-file (thin): size 20 GB of 20 GB,

     Guest OS shows 2,7 GB

Copy time from Datastore1 to Datastore2 with Datastore Browser: ~ 1:56 minutes

Another test with an other vmdk-file:

     vmdk-file (thick): size 5 GB,

     Guest OS shows: 1,6 GB

Copy time from Datastore1 to Datastore2 with Datastore Browser: ~ 34 secounds

I converted the vmdk in to thin format:

     vmdk-file (thick): size 2 of 5 GB,

     Guest OS shows: 1,6 GB

Copy time from Datastore1 to Datastore2 with Datastore Browser: ~ 54 secounds

I converted the vmdk back to thick format:

     vmdk-file (thick): size 5 GB,

     Guest OS shows: 1,6 GB

Copy time from Datastore1 to Datastore2 with Datastore Browser: ~ 34 secounds

This is strange. But i think it means, that the Browser only copy the real data and 'cp/mv' the hole file.

Why a converted file (thin -> thick) increase the copy time is serious.

[piaroa]

Correct the datastore browser will copy only used data, same for vmkfstools.