Stripe Width Questions

[Trey1234]

Hey people I've got a question about vSAN Storage Policies, specifically about stripe width.  To give some context, we have a 6 node all-flash (NVMe) vSAN cluster.  This is a brand new cluster running on Dell R740xd nodes with 3 disk groups per hosts.  We also have Deduplication and Compression turned on in the cluster.

I'm going to dumb this down a little bit but from what I understand, setting the stripe width on the vSAN Storage Policy will increase the amount of disks that data is striped across.  Theoretically this means that more disks are engaged which should increase performance. 

Now all that to get to my questions.  Why would you not increase the stripe width and at what point do you see negative returns from changing this setting?  A colleague of mine has set all our policies to use a stripe width of 7.  We have different policies for Raid-1, Raid-5, and Raid-6, all with 7 stripes.  This seems bad to me but I can't articulate why.  Does someone have test results that show how different stripe widths affect application performance?

[GreatWhiteTec]

We have done extensive testing with SW in many use cases, and typically we see little to no performance increases on all-flash configurations.

On the other hand, we have seen performance gains on Hybrid configurations given that spinning drives are slower, and the more spindles the better.

There is a breakeven point, and it will depend on the workload and configuration of VMs. For example, if you have an Oracle VM not properly configured (very few vmdks) then those objects MAY benefit from SW increase.

Stripe width policy changes should be considered on an object based level or VM, not for an entire cluster.

Also, if you want to have best performance then you should use Raid 1, as Raid 5 and Raid 6 have IO Amplification on writes (whether is vSAN or traditional storage).

Remember that SPBM is very flexible. You can have a VM with multiple vmdks. each of those vmdks can have different policies. For example, you have a VM with multiple vmdks, most vmdks (objects) require high performance, but two of those are cat videos and mp3s. You could assign a different policy to those objects (e.g. RAID5 or FTT=0) while the other vmdks have RAID1 FTT=1. We typically don’t recommend FTT=0 but that’s a story for a different day...