Today I will write about the virtual disk behavior on vSphere Big Data Extension where it relates to SCSI Controllers and Thin X Thick type of disks.
*** SCSI Controller ***
Every time you create a new BDE node the VM will present, at least, two
SCSI Controllers; one for the O.S and swap disks and another one for Data disks.
The O.S SCSI Controller will be the same as what’s already configured on
BDE Template, which by default is LSI Logical Parallel
Now, for the Data SCSI Controller, it will always be Paravirtual
SCSI Controllers (PVSCSI), which performs better in high I/O situations, like
Big Data systems, here’s the Paravirtual performance study case If you want to
read more about it.
Starting with BDE 2.3 you can specify controller type of O.S and swap disks:
- Change BDE’s template SCSI disk to Paravirtual and on BDE Server edit:
/opt/serengeti/conf/serengeti.properties
- Look for the following entry and adjust accordingly:
storage.system_swap.disk.controller.type=ParaVirtualSCSIController
- Restart tomcat
*** Disk Type ***
There was always discussion about disk performance between Thin and
Thick disks, while there’s definitely some performance benefits on Thick Earger
zeroed disks, it’s negligible, see the vStorage performance study here for more details.
To start with lest examine the O.S. disk; when you create a new node the
O.S disk type will be the same as the BDE Template, which by default it Thick.
TIP: I figured out if you Storage vMotion the BDE template to another
datastore and choose to convert the O.S disk to Thin, new nodes will also have
O.S Thin disks.
Now about Data Disk; When you configure the Datastores available for BDE
consumption will need to configure them as Local or Shared:
- Local mean for disks locally attached to the hosts ESXi;
- Shared mean for external disks managed by storage systems.
So, when you create a new BDE node on a Local datastore the data disks
will be Thick.
When you create a new BDE Node on a Shared datastore the data disk will
be Thin.
Well, nothing prevents you from setting up Local disks as Shared to have
Thin disks on the nodes, be aware that it could cause some vSphere HA issues;
BDE
might enables vSphere HA on nodes running on Shared disks, but since in reality
those disks are local, HA wont be able to restart the VM on another host in
case of host’s failure.
See you guys next.
