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VMware SIOC, first investigations

By default SIOC latency connention threshold is 30ms and is set per Datastore.
Only during contention, when the latency is greater than 30ms to a Datastore will SIOC start descheduling VM’s Disk queue access across the Hosts with Disk queues to that Datastore within vCenter.

SIOC recommendations:

• Ensure that datastores are managed by a single vCenter Server
• The storage media (spindles, SSD) on which the SIOC enabled datastores are located is not shared with volumes used by non-vSphere workloads.
• Storage I/O Control is supported on Fibre Channel-connected and iSCSI-connected storage. NFS
datastores and Raw Device Mapping (RDM) are not supported.
• SIOC not enabled on Datastores with multiple extents

This is the Technical Deployment considerations guide, great document how to implement SIOC:

How to troubleshoot issues:

vSphere Resource Management Guide:

Before using Storage I/O Control on datastores that are backed by arrays with automated storage tiering
capabilities, check the VMware Storage/SAN Compatibility Guide to verify whether your automated tiered
storage array has been certified to be compatible with Storage I/O Control. Automated storage tiering is the ability of an array (or group of arrays) to migrate LUNs/volumes or parts of LUNs/volumes to different types of storage media (SSD, FC, SAS, SATA) based on user-set policies and current I/O patterns. No special certification is required for arrays that do not have these automatic migration/tiering features, including those that provide the ability to manually migrate data between different types of storage media.


vSphere SAN compatibility guide:

SIOC feature is available with VMware vSphere 4.1T GA. SIOC is a QoS feature that is disabled by default. When enabled, this feature monitors ESX-array latency to determine when a datastore is congested. When congestion is detected (latency above a threshold), SIOC allocates the limited I/O resources to virtual
machines in accordance to their relative importance (user-specified). All the storage devices listed on vSphere 4.1 Storage HCL are supported for use with SIOC. There is no special certification requirements for the SIOC support.


SIOC Recommended Thresholds for Storage (mix of 50/50 SSD and FC should have threshold of 20ms, midpoint between the two types)

Chad Sakac recommends for EMC storage “the SIOC threshold should be the median between the slowest and fastest tier”

External I/O workload detected on shared datastore running SIOC errors:

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