Most failed virtual-NAS projects were decided before the install even started — the wrong disk choice, a host that sleeps at night, a datastore with no headroom. Ten minutes of honest planning first.
A DSM virtual machine is small, but it behaves like a real appliance that never sleeps. That changes what the host must provide: not peak power, but steady RAM, datastore headroom and genuine 24x7 uptime. And one decision — virtual disks or physical disks — is painful to reverse later, so it belongs here, before the VM exists.
👆 Check the host first — a DSM VM is small, but it runs all day, so RAM, datastore space and host uptime are the real requirements (figures are examples)
DSM itself is light. A lab VM runs well on 2 vCPU and 2 GB RAM, and 4 GB RAM makes package testing — Photos, Drive, a media indexer chewing through a test library — noticeably calmer. Storage is the real decision, covered in section 3. What hosts actually fail on is not CPU; it is uptime and space discipline. If the ESXi host is a PC that gets switched off at night, your NAS switches off with it. If the datastore fills up, every VM on it suffers, not just this one. Check both before you create anything.
Broadcom changed VMware licensing after acquiring the company, and the free ESXi situation has moved more than once — a free edition was withdrawn, then a limited free version was reported back for newer releases. The honest advice: check the current terms for your exact ESXi version before planning around them, because what was free last year may not be the offer today. Nothing in the DSM install depends on a paid tier; it needs only basic VM creation, SATA disks and a standard virtual switch.
You have three ways to give the VM storage, and changing your mind later means a rebuild:
For learning DSM, VMDKs are the honest default. Reach for RDM when you specifically want to rehearse a real-disk scenario.
Decide what this NAS is for before the first boot. Learning DSM, testing packages before touching a real box, rehearsing a migration, following this channel's Synology tutorials — all perfect. Storing the office accounts archive, the only copy of family photos, anything a business would cry over — not this, ever. DSM is Synology software, licensed for Synology hardware. Running it inside a virtual machine like this is a lab and learning exercise — some Synology services and packages may refuse to run or break, a DSM update can break the install, Synology support does not cover it, and it must never be the only place an office keeps its data. Write the lab's job on a sticky note, literally. It decides every later choice, especially backups and updates.
Watch the video for the host and VM preparation exactly as it was done for this install.
▶️ Watch Full Video2 GB runs DSM and its basic file services; 4 GB is the comfortable lab size if you will test heavier packages like Photos or Drive sync. More than that is rarely the bottleneck in a lab — disk and network usually are.
VMDK for a learning lab: portable, snapshot-friendly, simple. RDM when you deliberately want DSM to see a real physical disk with real SMART data — accepting that the disk becomes dedicated to this VM.
Broadcom changed VMware licensing after the acquisition and the free offer has moved more than once. Check the current terms for your exact version before relying on them — do not plan a lab around last year's licensing news.