An Important APD/PDL Change in the XtremIO Behavior
Hi
We have recently released a new target code for our arrays, know as XIOS 4.0.15
This release contains many fixes including a change in the APD/PDL behavior when using ESXi hosts, this is based on many customers feedback we have received that were asking to tweak the array APD/PDL behavior..
If you are new to this concept, I highly suggest you start reading about it here:
And an older article from the ESXi 5 days here, https://blogs.vmware.com/vsphere/2011/08/all-path-down-apd-handling-in-50.html
Permanent Device Loss (PDL) is a condition where all paths to a device are marked as “Dead.” Because the storage adapter cannot communicate to the device, its state is “Lost Communication.” Similarly, All Paths Down (APD) is a condition where all paths to a device are also marked as “Dead.”
However, in this case, the storage adapter displays the state of the device as “Dead” or “Error.”
The purpose of differentiating PDL and APD in ESX 5.x and higher is to inform the operating system whether the paths are permanently or temporarily down. This affects whether or not ESX attempts to re-establish connectivity to the device.
A new feature in XtremIO 4.0.15 allows the storage administrator to configure the array to not send “PDL” as a response to a planned device removal. By default, XtremIO configures all ESX initiators with the PDL setting.
In planned device removals where the cluster has stopped its services and there are no responses received by the ESX host for I/O requests, ESX Datastores will respond with PDL or APD behavior depending on the XtremIO setting.
An XMCLI command is used to enable all ESX initiators as “APD” or revert back to “PDL.” A new option is available for the modify-clusters-parameters admin-level command which modifes various cluster parameters:
device-connectivity-mode=<apd, pdl>
In any case, if you have a new or existing XtremIO cluster and you are using ESXi hosts (who doesn’t?), please set the initiators type to “ESX”
Refer to the XtremIO Storage Array User Guide (https://support.emc.com/products/31111_XtremIO/Documentation/) or
help in XMCLI for more information on its usage.
The version that will follow the 4.0.15-20 one will have APD turned on by default for newly installed arrays.