upgrading lab to SSD

[billdossett]

Hey, greetings...

I have a 4 node vsan cluster running vsphere 6.7 u2 in my lab.....  each node has a 256 SSD for cache and then 2 x 2TB hybrid disks for capacity.

2TB SSD disks have hit the sweet spot and I'm going to replace the the spinning disks..

What it the best way to go about this?  If I go to all SSD, do I need the cache any more?  Though i would like to keep as much capacity as possible, but would like to get away from the whole destaging process if possible - so thinking it would be nice to just take one node down replace the 2 x sshd + 1 ssd, with the two 2 TB SSDs and bring back online and let it rebuild.  This has been running for like 2 yrs now and I haven't had to do anything with it since the upgrade to 6.7.

Would appreciate any advice...

Regards

Bill

[VM_Yamato]

Is this your vSAN configuration?

Current setting - vSAN Hybrid

Node 01: [Cache 256GB*1][Capacity HDD 2TB*2]

Node 02: [Cache 256GB*1][Capacity HDD 2TB*2]

Node 03: [Cache 256GB*1][Capacity HDD 2TB*2]

Node 04: [Cache 256GB*1][Capacity HDD 2TB*2]

Goal setting - vSAN All flash

Node 01: [Cache 256GB*1][Capacity SSD 2TB*2]

Node 02: [Cache 256GB*1][Capacity SSD 2TB*2]

Node 03: [Cache 256GB*1][Capacity SSD 2TB*2]

Node 04: [Cache 256GB*1][Capacity SSD 2TB*2]

If yes, you can reconfigure existing Disk groups one by one.

>so thinking it would be nice to just take one node down replace the 2 x sshd + 1 ssd, with the two 2 TB SSDs and bring back online and let it rebuild.

When you shutdown your host, normally we use "maintenance mode" for target host. Then you can evacuate data from host that will be turned in to maintenance mode.

After that, please delete disk group inside the host -> remove 2 HDD from the chassis -> insert new SSDs -> Configure new Disk group -> exit maintenance mode.

Of course, don't forget to confirm your SSD is certified by vSAN on VMware Compatibility Guide.

VMware Compatibility Guide - vsan

Regards

[VM_Yamato]

Additional information.

Normally, above procedures is very major but if you would not like to turn on "maintenance mode" one by one, you can skip the host maintenace mode.

Migrating from Hybrid to All-Flash VSAN | Yellow Bricks

Regards

[IRIX201110141]

If I go to all SSD, do I need the cache any more?

Even with a AF vSAN you will have a "buffer" drive which takes all the writes, but no read caching anymore.

Regards,
Joerg

[VM_Yamato]

Yes, correct.

Hybrid vSAN     A cach drive in a disk group work as read and write cache. (70% read/30% write)

All flash vSAN   A cach drive in a disk group work as write cache only. (100% write buffer)

Write Caching | VMware vSAN Caching Algorithms | VMware

[billdossett]

Thank you for so much great information.... this is a lab, so I am going for low cost SSDs, I know how to mark drives as SSD even if they aren't recognized as such, so shouldn't be a problem... so I think if I got you, I want to put the host in the "full data migration" maintenance mode?  So then I delete the disk groups on the node, put my new disks in, leave the cache in place, power back up, create the new disk group and exit maintenance mode?   Does the rebuild take place automatically?  I have only replaced single failed disk in the past so this is new and interesting to me.  I've got an iSCSI target that I will clone all my VMs to just in case anyway, but would be nice to get it right first time!  Thanks Again, really appreciate it.

[VM_Yamato · Accepted solution]

Answer for each questions

■I want to put the host in the "full data migration" maintenance mode? 

>Yes you can. Normally, depends on following things, the data evacuation option you can use is changed.

1. what types of storage policy  you use.(FTT/Stripe and FTM)

2. Count of host in the cluster

Now you have 4 hosts and hybrid vSAN, so maybe you use “FTT-1 and RAID-1”, don’t you?

In the case, you can use “full data migration“.

■So then I delete the disk groups on the node, put my new disks in, leave the cache in place, power back up, create the new disk group and exit maintenance mode?  

Does the rebuild take place automatically? 

>Yes, correct. when vSAN cluster recognize available new host, automatically the rebuild will be starte.

Enjoy vSAN.

[billdossett]

Thanks, yes I have 4 nodes FTT-1 and RAID-1, it says I have 1.9 TB over the minimum need to do full data migration which seems right.

This is great, I can just do one node per day...

Thanks again, appreciate the help!