ansible-vplex library dellemc_vplex_device.py error on raid-0 creation

Hi EB_RB,

 

Let me answer the easy question first, YES, this is the right place to ask questions for Ansible Modules (for VPLEX in your case).

 

I do not have access to reproduce your issue, but I was looking at the product guide for more info on Create Device, Raid 0 and Extents.

I initially thought it only allowed raid-1 devices, since it  had this info on Page 22:

**********

Create a raid-1 device
To create a device, run the appropriate playbook.
The syntax of the task is shown as follows:

- name: Create raid-1 device
dellemc_vplex_device:
vplexhost: "{ { vplexhost}}"
vplexuser: "{ { vplexuser }}"
vplexpassword: "{ { vplexpassword }}"
verifycert: "{ { verifycert }}"
cluster_name: "cluster-1"
geometry: "raid-1"
device_name: "ansible-test"
extents: ["extent_1","extent_2"]
extent_state: "present-in-device"
state: "present"

 

The parameters must be set before the user runs the playbook. For more information about the parameters, see the Parameters
table.

******************************************

But when I looked at the Parameters table, I see you can change "geometry" to "raid-0" as well as

"extent_state" to "present-in-device" or "absent-in-device"

 

Since the error has to do with Extents, and since the add/remove extent section says this is ONLY support on raid-1 devices:

*****

NOTE: This task is supported only for raid-1 device. It is not supported for raid-0 and raid-c devices.

*****

 

Is it possible when you created the raid-0 device that you had the parameter extent_state set to  "present-indevice" instead of "absent-indevice"?  This is an optional parameter, so I don't know if it was used or not.

Can you share your parameter list?

Also, if others would like to comment (and reproduce the issue maybe?), that would be great!

 

Hi and thanks to help me.

In the docstring section of the dellemc_vplex_device.py, there is an example for raid-0 creation. This example is missing into the pdf documentation.

- name: Create a new raid-0 device
     dellemc_vplex_device:
       vplexhost: "{
 {
  vplexhost }}"
       vplexuser: "{
 {
  vplexuser }}"
       vplexpassword: "{
 {
  vplexpassword }}"
       verifycert: "{
 {
  verifycert }}"
       cluster_name: "cluster-1"
       geometry: "raid-0"
       stripe_depth: "1KB"
       device_name: "ansible_device"
       extents: ["extent_0", "extent_1"]
       extent_state: "present-in-device"
       state: "present"

Here is my call to the module :

To create a device you need to specify an extent.

A device is always created on top of an extent, I think you cannot create an "empty" device. So the "extents" parameter is mandatory

- name: "Managing device on vplex c1"
  dellemc.vplex.dellemc_vplex_device:
    vplexhost: "{
 { block_system_matrix['i']['vplex'] }}" # the name of the cluster vplex mgmt
    vplexuser: "{
 { emc_vplex_user }}"
    vplexpassword: "{
 { emc_vplex_password }}"
    verifycert: no
    cluster_name: "{
 { block_system_matrix['i']['cluster_vplex'] }}" # cluster-1 or cluster-2
    geometry: "raid-0"
    stripe_depth: "4KB"
    device_name: "d_{
 { unity_vol_c1.volume_details.name }}_c1" # the name of the device to be created
    extents: ["e_{
 { unity_vol_c1.volume_details.name }}_c1"] # the extend on which we are creating the device
    extent_state: "present-in-device"
    state: "present"
  

 

When i restart the job without "extent-state", there is an error : as specified in the example this argument is missing :

fatal: [localhost]: FAILED! => {"changed": false, "msg": "parameters are required together: extents, extent_state"}

When i restart the job without "extents" end "extent-state", the module try to make a get of the device according the doc and it doesn't find the device that we want to create.

fatal: [localhost]: FAILED! => {"changed": false, "msg": "Could not get device d_SAMAQ001_TESTEBO_DLG_BUILD_S_120_c2 in cluster-2"}

 

When I restart the job with "extent" and "extent-state" and "absent-in-device", the module try to get the device to remove this extent, but the device don't exists :

fatal: [localhost]: FAILED! => {"changed": false, "msg": "Could not get device d_SAMAQ001_TESTEBO_DLG_BUILD_S_120_c2 in cluster-2"}

 

Hi eb_rb,

I was able to confirm with the rest of the product team that this is in fact a bug when creating a RAID-0 device that contains multiple extents.  A fix is being investigated and will likely be targeted for the Q12021 release.

On a side note, I'm curious what is driving the need to create a RAID-0 (striped) device.  Based on my experience most users tend to use 1:1 mapping of storage volumes all the way through to the virtual volume or use RAID-1 to have a mirrored local copy of the data.

Thanks
Bryan

Hi Bryan,

Ok for the fix.

For the device raid geometry, in this case, I'm automating creation of block storage and I base myself on the existing raid-0 geometry on all local-device into vplex.

So now, I'm looking for more informations about that : in the 6.2 documentation (admin guide, cli guide) it seems that nothing explain the different geometry options.

I've find in 5.2 (!) documentation these explanations :

VPLEX supports the following RAID types:
◆ RAID-0 - Stripes data across two or more storage volumes.
RAID-0 devices provide better performance since data is retrieved from several
storage volumes at the same time. RAID-0 devices do not include a mirror to
provide data redundancy.
Use RAID-0 for non-critical data that requires high speed and low cost of
implementation.
◆ RAID-1 - Mirrors data using at least two devices to duplicate the data. RAID-1
does not stripe.
RAID-1 improves read performance because either extent can be read at the same
time.
Use RAID-1 for applications that require high fault tolerance, without heavy
emphasis on performance.
◆ RAID-C - Appends (concatenates) extents or devices into one larger device.

 

When you read this, there is no recommandations about 1:1 mapping.

No option match with the fact that you want to do 1:1 mapping ( 1lun, 1svol, 1extent, 1device), so it seems that no option is better or worse.

Can you develop what you mean by 1:1 mapping option related to device geometry please ? What could a geometry change bring and to wich geometry ?

 

The options to have multi-extent RAID-0 and RAID-C devices have been somewhat discouraged in recent years due to the complexity and overlap with functionality on the underlying backend arrays.

For the 1:1 mapping you can just create a RAID-0 device with only one extent and use that device as the basis for a virtual volume.

Hope that makes sense.  For troubleshooting and understanding/simplification of the I/O path it makes things easier.

Thanks
Bryan