I spent a good portion of my career moving storage from one array to another. The driver is normally something like this:
- Cost of older array (life cycle time)
- New capacity, speed or feature
So off we went on another interruption migration of lun’s and data.. At one point I was sold on physical storage virtualization appliances. They stood in front of the array and allowed me to move data between arrays without interruption to the WWID or application. I loved them what a great solution. Then storage vMotion became available and 95% of the workloads were running in VMware. I no longer needed the storage virtualization appliance and my life became very VMware focused.
New Storage paradigm
With the advent of all flash arrays and HCI (all flash or mixed) performance(speed) has almost gone away as a reason for moving data off arrays. Most arrays offer the same features; replication capability aside. So now we are migrating to new arrays / storage shelf’s because of capacity or life cycle issues. Storage arrays and their storage shelves have a real challenge with linear growth. They expect you to make a bet on the next three years capacity. HCI allows a much better linear growth model for storage.
My HCI Gripe
My greatest grip with HCI solutions is that everyone needs more storage that does not always mean you need more compute. Vendors that provide hardware locked (engineered) platforms suffer from this challenge. The small box provides 10TB, Medium 20TB and large 40TB. Which do I buy if I need 30TB? I am once again stuck in the making a bet problem from arrays (at least it’s a smaller bet). The software based platforms including VSAN (full disclosure – At time of writing I work for VMware and have run VSAN in my home for three years) have the advantage of offering better mixed sizing and linear growth.
What about massive growth?
What happens when you need to double your storage with HCI and your don’t have spare drive bays available? Do you buy a new set of compute and migrate to it? That’s just a replacement of the storage array model… Recently at some meetings a friend from the Storage and availability group let me know the VSAN solution to this problem. Quite simply replace the drives in your compute with larger drives in a rolling fashion. You should create uniform clusters but it’s totally possible to replace all current drives with new double capacity drives. Double the size of your storage for only the cost of the drives. (doubling the size of cache is a more complex operation) Once the new capacity is available and out of maintenance mode data is migrated by VSAN on to the new disks.
What is the process?
It’s documented in chapter 11 of the VSAN administration guide : https://pubs.vmware.com/vsphere-60/topic/com.vmware.ICbase/PDF/virtual-san-600-administration-guide.pdf
A high level overview of the steps (please use the official documentation)
- Maintenance mode the host
- Remove the disk from the disk group
- Replace the disk you removed with the new capacity drive
- Rescan for drives
- Add disk back into the disk group