Slow Write Speeds on NVMe

[VioSpeed]

Anyone able to help on why I'm getting such slow write speeds on an NVMe drive in a Windows 11 VM? I benchmarked this drive before I installed it into a Proxmox machine and was getting 5000+ MB/s write speed.

I'm running the VirtIO SCSI single controller with the latest VirtIO drivers.

 

[cheiss]

Hi,

first of, CrystalDiskMark is not a good, indicative benchmark overall.
Secondly, what filesystem are you using (both on the host and in the VM), as well as what disk model do you have exactly? I could imagine it's some sort of consumer SSD?

More over, did you already see our Windows 10 guest best practices guide?
For the hard disk, I would e.g. recommend using also virtio, not SCSI.

 

[VioSpeed]

Hi,

first of, CrystalDiskMark is not a good, indicative benchmark overall.
Secondly, what filesystem are you using (both on the host and in the VM), as well as what disk model do you have exactly? I could imagine it's some sort of consumer SSD?

More over, did you already see our Windows 10 guest best practices guide?
For the hard disk, I would e.g. recommend using also virtio, not SCSI.

I'm running ZFS for the host and LVM for the VMs. I use a Samsung 980 EVO which is gen3 PCIE. Just checking the specs and it states it can do up to 3000MB/s writes.

I just checked your Windows 10 best practice guide and changed the cache to writeback and ticked the discard box. I'm not sure how to change the hard disk from SCSCI to virtio when the VM has been created?

 

[cheiss]

I use a Samsung 980 EVO

These are mediocre consumer SSDs without DRAM and PLP. Also, the firmware on Samsung drives also needs updating in some cases to remedy quick failure rates.

The numbers that the manufacturer specifies and that CrystalDiskMark show are normally burst-numbers for show, which are maybe achievable in perfect conditions until the internal cache is full. Esp. with ZFS this happens very fast due to Copy-On-Write, after which such SSDs just degrade very quickly in performance.
Windows is also generally very I/O heavy.

You can search around in the forum, there a tons of threads on this topic.

I'm not sure how to change the hard disk from SCSCI to virtio when the VM has been created?

It could work to install the VirtIO drivers inside the VM and then switch the drive type, although Windows is very finnicky and cannot really deal with such changes, I think.

 

[VioSpeed]

These are mediocre consumer SSDs without DRAM and PLP. Also, the firmware on Samsung drives also needs updating in some cases to remedy quick failure rates.

The numbers that the manufacturer specifies and that CrystalDiskMark show are normally burst-numbers for show, which are maybe achievable in perfect conditions until the internal cache is full. Esp. with ZFS this happens very fast due to Copy-On-Write, after which such SSDs just degrade very quickly in performance.
Windows is also generally very I/O heavy.

You can search around in the forum, there a tons of threads on this topic.


It could work to install the VirtIO drivers inside the VM and then switch the drive type, although Windows is very finnicky and cannot really deal with such changes, I think.

Okay great thanks. Is there a guide for TrueNAS best practise settings with setting up a VM like the Windows 10 one you linked me? I have PCI passthrough enabled for a HBA and x8 mechanical drives and would like to maximise the performance.