This is a
common question the SC/SA group often hears from the end-user community. Over time and after multiple customer
deployments using EqualLogic and VMware, we have come to understand specific
considerations and guidelines to help determine the right mix of vm's to
volumes/datastores. Additionally, VMware has continued to make huge leaps in
optimizing the storage IO and ESX relationship.
ground rules. Although there is an absurdly upper maximum of 3011 vm's in a
single VMFS datastore, in practice, it is much lower. In most cases, it is the
underlying storage array(s) that will dictate the performance of the VMFS
datastore and the vm's that reside within them. This brings up the topic of
ESX's storage queues. The default value can be increased but 128 should be
sufficient in nearly all cases. Placing multiple vm's within a volume/datastore
will result in the vm's sharing the device queue, whereas a single vm within a
single datastore will have complete and uninterrupted access to the queue. Although structuring your storage by creating
a 1:1 relationship for volume->datastores->vm may be good for 1 vm, it
may decrease overall performance as well as create a large number of VMFS datastores,
iSCSI connection counts, and management overhead. So, the end result is: keep
it simple and leave the defaults in place.
important improvement in vSphere over previous releases is the ability to drive
more throughput from the ESX host to a VMFS datastore. In VI3 Infrastructure,
the maximum throughput from a given ESX host to an iSCSI target was limited to
1Gb due to the single TCP session limitation in the vmkernel iSCSI initiator.
Today, vSphere users can accomplish multiple threads and TCP sessions from ESX
to target and leverage native path management techniques such as Fixed, Most
Recently Used, Round-Robin, and in EqualLogic environments, Path Selection
Plugins (PSP) providing Windows-like MPIO connection load balancing. Furthermore,
10Gb Ethernet provides an abundant of options and, when properly constructed
with Storage IO Controls (SIOC) found in vSphere 4.1, can really enhance
beginning with vSphere4.1, scalability of VMFS datastores were further enhanced
with the vStorage API for Array Integration (VAAI). Previous releases faced the
real possibility of a SCSI reservation/locking issue during certain operations
(vm snapshot, for example)). In large-scale vm deployments, locking a resource,
even for a minute, is unacceptable.
is this: you are not limited by any hard rule other than the configuration and
type of storage. With EqualLogic using firmware version 5.x or above, the
arrays fully support VAAI and scale very easily to accommodate any capacity or
disk IO need. Additionally, EqualLogic
provides in-depth SAN monitoring tools with SANHQ to allow administrators to
track and monitor how the virtual datacenter is performing.
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