Increasing datastore capacity: how long?

[BHagenSPI]

I "inherited" an older 5.5 environment. It has several 2TB datastores attached to each host (HITACHI Fibre Channel Disk) that are all pretty much filled up. There's also a 20TB datastore connected via iscsi that isn't being used at all. Because a couple VMs had ground to a halt due to their datastores running out of space, I migrated storage on 3 of them to the huge datastore...and *then* started investigating what exactly this thing is!

I found that the 20TB datastore is attached to each host (MSFT iSCSI Disk) and pointing to a windows 2012R2 server that has a 32TB iscsi virtual disk. For some reason, only 20 of the 32TB was used for this (virtual) disk, so I expanded it to the full 32TB. It took almost 3 days. 🙂

Now if I go into vsphere (web client): datastore, manage, settings, general, capacity, increase, I can click the lun, specify configuration, datastore details, drop down the partition configuration, and "use 'Free space 12.70TB' to expand the datastore" is a choice.

My questions are:

1. How long is it going to take to expand the datastore from 20TB to 32.7TB?

2. Will this impact performance at all?

Unfortunately, the vm's now using storage on the 20TB datastore are critical and can't be down for more than 4hrs, between 9pm-1am, so I do *not* want to inadvertantly take any of them down during this process.

Thanks!

[Krenztor · Accepted solution]

I haven't expanded a datastore to that large of a size before so I can't off anything really authoritative but for the smaller datastores that I've increased (usually from 2 TB to something closer to 8 TB) the increases happen almost instantly and I don't believe any of my VMs were affected during these changes.

If you want to watch a quick video on what to expect when you do an increase see this video here.

https://www.youtube.com/watch?v=qy1tbkh9Yqk

[Finikiez]

Hello!

It won't take much time if there are no issues with connectivity between ESXi hosts and your iSCSI target. It should take just several seconds.

No performance impact on running VMs.

Because all that happens is that you modify informtion about the end of your VMFS partition. Nothing more.

[BHagenSPI]

I bit the bullet and began the process at the beginning of the 4 hour window last night and...it took about 12 seconds. 🙂

Now I have 32.7TB available and am already migrating VMs to it.

Thanks for the responses!