TVS-473: m.2 cache for virtualization

[Trexx]

I was happy to read that caching is block level, but am surprised to read that caching didn't result in noticeable performance gains for guest operating systems. I suppose that once loaded, there really aren't repeated reads and that it might help a little with random writes.

Think about the initial data flow ... NAS Disk (read) -> m.2 Cache (storage) -> VM (memory). Unless you are re-reading that block frequently (say due to swapping due to insufficient VM memory), you aren't going to be hitting it a lot. Now if say that block was part of a SQL Database running on a VM that you were doing frequent queries against, then you would likely see more benefit. Also remember that the cache covers ALL Volume reads, not just for VM's so that block could get bumped out of cache by other NAS usage potentially.

A couple of more questions about virtualization: If I provision a 200GB VM, does that immediately create a 200GB file or will it simply grow up to the maximum of 200GB? Can I provision the VM on spinning disks today and move it to a m.2 volume later? Are there any drawbacks to running VMs on a m.2 volume? Does wear or heat play a role when using m.2 like this?

The .img file for the VM data will grow to the file limit. It doesn't pre-allocate all the space at once. As for moving the file, yes you could do it, but remember the m.2's are configured for a specific usage. So if you configure them as cache, then you can't also use the same m.2 as SSD Storage.

As for wear/heat, there is a finite lifespan to SSD's in general, and if you put them under heavy load the memory chips/controller on the m.2's can get hot. They do have thermal protection to keep them from "melting" but that also then slows down performance. Good ventilation around the NAS and potentially even installing heat-sinks on the m.2's can help the heat issue, but the heat sinks may void your warranty on the m.2 depending brand so check with the manufacturer.

On the note of using UPS, I fully agree and have 3 in my home alone. I've always found the tricky part is getting the UPS to notify the devices to gracefully shutdown before the batteries run out.

As long as it is a model that connected via USB and on QNAP's compatibility list, you should be fine on the graceful shutdown.

My TVS-473 was delivered today - I can't wait to start using it so that I can retire my ~8 year old PC/server! The 16GB sticks are en route, but I think I'll wait on the m.2 until I get a better feel for performance.

Thank you all for your valuable input. It's much appreciated and ultimately resulted in me buying into the QNAP platform!

--
Marc

Enjoy your 473 Marc. Read the online documentation as well as getting started tutorials. You may want to play around a little bit to get the feel of things before you start moving too much data over. Make sure and have an external USB drive for backups. While RAID helps prevent data loss, it is not guarantee.

[QNAPDanielFL]

If you provision 200GB for your VM then only the amount that VM actually uses will be taken up on your nas. Even if you provision 200GB for your VM, your Nas will see that VM as a file that is the size the VM actually uses. This is because VMs on your nas benefit from thin provisioning. Then the limit on the space your VM can take is 200GB but that much is not taken up unless the VM grows in size.

You can move a VM from a spinning disk to an SSD volume. One possible drawback of M.2s is they are more prone to overheat than normal SSDs. But you can install a heat sink on them.

[storageman]

If you provision 200GB for your VM then only the amount that VM actually uses will be taken up on your nas. Even if you provision 200GB for your VM, your Nas will see that VM as a file that is the size the VM actually uses. This is because VMs on your nas benefit from thin provisioning. Then the limit on the space your VM can take is 200GB but that much is not taken up unless the VM grows in size.

You can move a VM from a spinning disk to an SSD volume. One possible drawback of M.2s is they are more prone to overheat than normal SSDs. But you can install a heat sink on them.

Really? Surely that depends if your underlying volume is thin provisioned?

[QNAPDanielFL]

My understanding is that VMs on Qnap devices always use thin provisioning in how space is allocated for each vm. Even if you have set your NAS to thick provisioning or just one volume the VMs will benefit from thin provisioning.

[Trexx]

There is NO thin provisioning at a QNAP Storage Pool/Volume Level related to the VS.

QNAP VS is based on QEMU. VS 3.x versions (and possibly earlier) leverage QEMU's QCOW2 (QEMU copy-on-write) format.

qcow2 is the main format for disk images used by QEMU. One of the features of this format is that its size grows on demand, and the disk space is only allocated when it is actually needed by the virtual machine.

https://blogs.igalia.com/berto/2015/12/ ... -l2-cache/

The QCOW2 image file will "grow", as your VM's file space usage grows, up to the max size specified when you created the HDD in VS.

[FogDucker]

I was very happy to see that it grows on demand! My bare bones Windows 7 VM is consuming only 15GB of 245GB allocated and I was easily able to move it from one volume to another. Very impressive! Moving to SSD will be simple once I get them.

Coming from a Synology, the only thing I was disappointed with is that there is no native mail server application included. I grew used to running a local IMAP server to archive my mail to. I could add this functionality to a VM, but decided to low-tech it and use Mailstore.

Another few days of testing/experimenting before I reset my QNAP and start all over with a final configuration.

[Trexx]

If you are thinking of using the SSD's for QTier, that can ONLY be setup at time of Storage Pool creation. There is no retro-fit option.

For SSD caching, or just general Storage Pool/Volume SSD usage, you can set that up after you setup your 1st storage pool.

[storageman]

There is NO thin provisioning at a QNAP Storage Pool/Volume Level related to the VS.

QNAP VS is based on QEMU. VS 3.x versions (and possibly earlier) leverage QEMU's QCOW2 (QEMU copy-on-write) format.

qcow2 is the main format for disk images used by QEMU. One of the features of this format is that its size grows on demand, and the disk space is only allocated when it is actually needed by the virtual machine.

https://blogs.igalia.com/berto/2015/12/ ... -l2-cache/

The QCOW2 image file will "grow", as your VM's file space usage grows, up to the max size specified when you created the HDD in VS.

Thanks for clarification but to be clear what happens to the underlying volume?
Say you have used 10GB of a 100GB sized allocated VM, is the underlying volume free's space reduced by 100GB (when the VM first created) or just 10GB as this is the used space to date.

[Trexx]

Thanks for clarification but to be clear what happens to the underlying volume?
Say you have used 10GB of a 100GB sized allocated VM, is the underlying volume free's space reduced by 100GB (when the VM first created) or just 10GB as this is the used space to date.

Just the space used to date (10GB in your example).

[aarbee]

For the good order, I have received my UPS today.
Back-UPS Pro BR900G-GR

The Qnap says that it is good for +/- 3 hours.

[Trexx]

NIce!

[aarbee]

Is a bit heavier then I thought (bought the 900VA and I thought I had bought the 700VA...)
I have placed the 673 on a lower shelf, and placed the hot switch (yup you can bake an egg on it), a shelf higher. Resulting in dropping the fans from 70% to 40% and a dropping temp for the M2 from 49C (118F) to 40C (104F).
The cooling fins are still not installed. Going to wait until the end of the month.

[Trexx]

Is a bit heavier then I thought (bought the 900VA and I thought I had bought the 700VA...)
I have placed the 673 on a lower shelf, and placed the hot switch (yup you can bake an egg on it), a shelf higher. Resulting in dropping the fans from 70% to 40% and a dropping temp for the M2 from 49C (118F) to 40C (104F).
The cooling fins are still not installed. Going to wait until the end of the month.

If you are at 40c under load on the m.2s, you don't need the heatsinks.


Sent from my iPhone using Tapatalk

[aarbee]

Just checked it. Read was at 0% and write at 100%. Not sure if that is called under load.
I would like to go to an automated RPM on the fans. Will test and see what it does do.

[Trexx]

Just checked it. Read was at 0% and write at 100%. Not sure if that is called under load.
I would like to go to an automated RPM on the fans. Will test and see what it does do.

That's your cache acceleration hit rates. You want to check your m.2 temperatures while you doing a large file copy (GB range) from your PC to NAS.