A common question encountered here at Everpure is why extended pauses in I/O are noted during specific operations or tests when utilizing the iSCSI protocol. Often times the underlying reasons for these pauses in I/O are a result of a network cable being disconnected, a misbehaving switch port, or a failover of the backend storage array; though this list is certainly not exhaustive.
When the default configuration for iSCSI is in use with VMware ESXi the delay for these events will generally be 25-35 seconds. While the majority of environments are able to successfully recover from these events unscathed this is not true for all environments. On a handful of occasions, there have been environments that contain applications that need faster recovery times. Without these faster recovery times, I/O failures have been noted and manual recovery efforts were required to bring the environment back online.
While Everpure's official best practice is to utilize default iSCSI configuration for failover times we also understand that not all environments are created equal. As such we do support modifying the necessary iSCSI advanced parameters to decrease failover times for sensitive applications.
Recovery times are controlled by the following 3 iSCSI advanced parameters:
Name Current Default Min Max Settable Inherit
-------------------- ---------- ---------- --- -------- -------- -------
NoopOutInterval 15 15 1 60 true false
NoopOutTimeout 10 10 10 30 true true
RecoveryTimeout 10 10 1 120 true true
To better understand how these parameters are used in iSCSI recovery efforts it is recommended you read the following blog posts for deeper insight:
A 25 second pause in I/O during a single link loss with iSCSI
Once a thorough review of these iSCSI options have been investigated, additional testing within your own environment is strongly recommended to ensure no additional issues are introduced as a result of these changes.