Storage DRS trying to move all VM's to one datastore that's already over provisioned very low on space?

[fourg]

We have a couple datastore clusters and I'm exploring the option to automate Storage DRS on one of them. This datastore cluster consists of five datastores, but all that Storage DRS does is recommend to move around ~500GB of VM's over to one of the five datastores which is overprovisioned by 500GB already and has 48GB of space free. These datastores are all being served up in the same method via iSCSI. What am I missing?

[DanielOprea]

Hi, please look to this articles and to the PDF:

http://www.josemariagonzalez.es/2009/03/08/modulo-6-configuracin-iscsi-ha-drs-storage-vmotion-en-vi3...

http://www.yellow-bricks.com/2012/05/22/an-introduction-to-storage-drs/

http://www.vmware.com/files/pdf/iSCSI_design_deploy.pdf

[fourg]

I have a handful of other datastore clusters which operate as expected, however this one datastore cluster thinks that all VM's should be moved to a datastore which is literally almost out of space.  The only thing I could think of right now is if a reboot of vCenter might help. 

[corvettefisher]

What is the latency of the datastores? Keep in mind DRS is looking at both Latency and space utilization.

Increasing the latency threshold to 20ms may help counterbalance this, as from the picture you've posted it appears the threshold is at 15 ms and some VM's seem to be exceeding that.

[fourg]

The I/O latency on the source datastores range from 8ms up to 15.5ms.  I tried bumping up the threshold up to 20ms, but not seeing any difference in the recommendations to move all the VM's over to this one low space datastore.  As you'll see in my original screenshot the reason for the recommendation is stated as "Balance datastore space usage", not anything regarding latency.  It's as though vCenter thinks the other datastores are all out of space.

[DanielOprea]

Hy,

Please look to this book:

http://www.vmware.com/files/pdf/vmw-vsphr-5-1-stor-drs-uslet-101-web.pdf

vSphere 5.0 Storage Features Part 5 - Storage DRS - Balance On Space Usage | VMware vSphere Blog - V...

[vThinkBeyondVM]

Whether your datastores are co-related ? If they are, SDRS does not recommend to migrate VMs on such datastores:

Refer:Storage DRS datastore correlation detector - frankdenneman.nl

Also, whether your datsstores are procured as thin provisioned. SDRS does behave differently here as well.

Note that if migrating VMs on particular datastore to balance space load is leading to IO imbalance or vice-versa, SDRS does not recommend such datastore. It computes cost and benefit it can get, if the benefit is more than cost, it does recommend otherwise NO.

Please if you have any SDRS affinity/anti-affinity rules configured.  Rules does impose constraint on SDRS load balancing abilities.

What else you can try is: Just disable IO metric, Now SDRS will only consider space & see how SDRS does behave. If it is still recommending to migrate on over provisioned datastore, then there can be a problem.

Please let me know which VC/ESXi release you are on ? if possible provide build numbers?