Hi!
Welcome to the forum!
Lots of questions there so let’s try and break these out and help, the main issue we’ll have is there are a fair few manufacturers out there so we can only advise with the ones we’re familiar with.
I couldn’t see a mention of Hyper-V vs VMware for this, so I’ll be giving generic advice that applies to both.
I primarily deal with Dell for infrastructure and the best option for something like this IMO is the Dell PowerEdge R740XD, but it gives you a good idea of what’s possible and what to look for in your preferred vendor.
Most Dell servers have the option of a BOSS (Boot Optimised Storage Solution). This is a RAID 1 two drive system used for the OS of the physical device. Now Dell don’t support VMware on SD cards, BOSS makes the most sense here. Especially if you’re using Hyper-V the ability to boot from SSD will help maintain performance.
The Dell R740XD has multiple chassis configurations, you haven’t mentioned actual required performance numbers here so the odds are you’ll have some clients with more demands than others, or some that have a higher standard of performance expectation for DR. The chassis configurations available allow you to use either sole use of or a mixture of NVMe, 2.5” SSD/HDD or 3.5” SSD/HDD. This will allow you to potentially consolidate replication and backup to the same device. If so you could look at a creating a RAID 60 volume based out of traditional spinning disks (or if the data set was small enough you could look at flash storage) whilst using faster SSD/NVMe RAID array for the replication target, with spare disk capacity remaining within the chassis.
If you’ll require more storage than a single server would require but want to keep it as close to a single unit as possible, you could use a single server + a storage shelf via the use of a SAS card to something such as a Dell PowerVault MD1400/1420 to tier out as necessary.
The Dell R740XD supports 1 or 2 CPUs, so you can give yourself expansion room by spec’ing a decent single CPU if that fits your requirements and know you can simply add a second should the customer require it. RAM is of course also configurable…
The R740XD supports up to 100GbE networking so regardless of the switching your clients are using you can find a NIC that will ensure this device won’t be the bottleneck.
Now that the server spec discussion is out of the way, onto your remaining questions:
If you want to start a VM that has been replicated(via traditional or CDP), the storage that the VM was replicated to is the storage that will be used for all of the change tracking. If you’re spinning up a backup however you need to specify either a vPower NFS share (VMware only) to keep the changes on, or a target datastore that the changes can be written to (this datastore needs to be visible within ESXi if you’re using VMware as your platform).
Replication will give you better performance than backup recovery and it can start immediately, that is because the VMs are registered in your target Hypervisor server and are stored uncompressed, ready to start.
Backups on the other hand are compressed and deduplicated to save space, so when you want to restore the entire VM to your DR server you have two options, either a full VM restore which will take potentially a long time but the VM will run faster once restored because its then running natively on the Hypervisor. Alternatively you can use Instant VM recovery which will run the VM from the backup, provided you have a datastore it can save the changes to (see comments above about this or vPower NFS for VMware), this will be slower performance and incur more resource penalties as a result (CPU/RAM requirements to read from the backup etc).
When sizing this DR host don’t forget to size your Veeam components accordingly, the Veeam help Center documentation will tell you the minimum you’ll need for Veeam B&R itself, if you’re using monitoring such as Veeam One, the specs for that, the specs required for proxy (data processing) /repository (data read/writing) roles.
Hopefully this has been helpful, even if a long post! Some of the things I’ve mentioned may have triggered more questions so please don’t hesitate to follow up with further questions as you think of them!
