Hello All,

I run a home lab currently that is based on Windows Server 2016. I have found lately that my storage spaces solution that is using tiered storage with an ssd and 3 hdds is really slow. I have tested using unraid so far at home with 2 cache ssds and 3 mechanicals and crystal mark shows much better reads and writes of 1200 vs 300 mbps. For space savings, while watching the 7 gamers 1 cpu video again, Linus (Linus Tech Tips) mentioned about using BTRFS to snapshot and boot off that with changes being kept in the dedicated drive for the machine to save space. I am having trouble finding information on how to do that. Does anyone know where I can find that information or what it is?

You just snapshot the vdisk and point the VM to use the new snapshot as the vdisk, though if it's a one time thing you can just use cp --reflink, either can only be done using the CLI for now, more info here:

https://forums.unraid.net/topic/51703-vm-faq/?do=findComment&comment=523800

 

14 hours ago, johnnie.black said:

You just snapshot the vdisk and point the VM to use the new snapshot as the vdisk, though if it's a one time thing you can just use cp --reflink, either can only be done using the CLI for now, more info here:

https://forums.unraid.net/topic/51703-vm-faq/?do=findComment&comment=523800

 

Thank you. That was helpful. Getting a little stumped on it and not sure if I am doing something wrong. So I created a new share to save VMs in and set it to be Auto for Cache-on-Write (don't have a yes option) which is set to prefer cache. My cache drives and array drives are all BTRFS. When I try those commands though it seems like I keep getting messages that it already exists but dosn't show in the list and I can't create it. Am I doing something wrong?

 

Here is what I was running in CLI via the web terminal:

 

root@Storinator:~# btrfs subvolume create /mnt/user/domains
ERROR: target path already exists: /mnt/user/domains
root@Storinator:~# btrfs subvolume snapshot /mnt/user/domains/1060 /mnt/user/domains/1060bak
ERROR: Not a Btrfs filesystem: Invalid argument
root@Storinator:~# btrfs subvolume snapshot /mnt/user/domains /mnt/user/domains_bak
ERROR: Not a Btrfs filesystem: Invalid argument
root@Storinator:~# btrfs subvolume snapshot /mnt/cache/domains/1060 /mnt/cache/domains/1060bak
ERROR: Not a Btrfs subvolume: Invalid argument
root@Storinator:~# btrfs subvolume create /mnt/cache/domains/1060
ERROR: target path already exists: /mnt/cache/domains/1060
root@Storinator:~# btrfs subvolume snapshot /mnt/cache/domains/1060
btrfs subvolume snapshot: too few arguments
usage: btrfs subvolume snapshot [-r] [-i <qgroupid>] <source> <dest>|[<dest>/]<name>

    Create a snapshot of the subvolume

    Create a writable/readonly snapshot of the subvolume <source> with
    the name <name> in the <dest> directory.  If only <dest> is given,
    the subvolume will be named the basename of <source>.

    -r             create a readonly snapshot
    -i <qgroupid>  add the newly created snapshot to a qgroup. This
                   option can be given multiple times.

root@Storinator:~# btrfs subvolume snapshot /mnt/cache/domains/1060 /mnt/cache/domains/1060bak
ERROR: Not a Btrfs subvolume: Invalid argument
root@Storinator:~# btrfs subvolume list /mnt/cache
root@Storinator:~# btrfs subvolume create /mnt/user/VMs/1060
ERROR: target path already exists: /mnt/user/VMs/1060
root@Storinator:~# btrfs subvolume list /mnt/cache
ERROR: cannot access '/mnt/cache': No such file or directory
ERROR: can't access '/mnt/cache'
root@Storinator:~# btrfs subvolume list /mnt/user/VMs
ERROR: not a btrfs filesystem: /mnt/user/VMs
ERROR: can't access '/mnt/user/VMs'
root@Storinator:~# btrfs subvolume list /mnt/cache/VMs
root@Storinator:~# btrfs subvolume create /mnt/cache/VMs
ERROR: target path already exists: /mnt/cache/VMs
root@Storinator:~# btrfs subvolume list /mnt/cache/VMs
root@Storinator:~# btrfs subvolume snapshot /mnt/cache/VMs /mnt/cache/VMs_backup
ERROR: Not a Btrfs subvolume: Invalid argument
root@Storinator:~#

17 minutes ago, TheArtiszan said:

root@Storinator:~# btrfs subvolume create /mnt/user/domains
ERROR: target path already exists: /mnt/user/domains

The subvolume path must not exist already, i.e. you create one and that will be your share, also you need to use the disk share, not the user share, use for example: /mnt/cache/domains

3 minutes ago, johnnie.black said:

The subvolume path must not exist already, i.e. you create one and that will be your share, also you need to use the disk share, not the user share, use for example: /mnt/cache/domains

Yeah. After playing with it some more I found that I was actually trying to create a btrfs subvolume to a directory that already existed. That looks like what my problem was there. Real head desk moment. Thanks for the help. Trying to copy into it now and see how things work.

Then I just need to make copies of the snapshot for each VM to use then.  Like from the backup to the new directory for the new VM?

You can just make a copy using cp --reflink like explained in the link above, and you don't even need subvolumes or snapshots for that, or take a snapshot then have the new VM use it.

19 minutes ago, johnnie.black said:

You can just make a copy using cp --reflink like explained in the link above, and you don't even need subvolumes or snapshots for that, or take a snapshot then have the new VM use it.

I think this is starting to make sense to me. So after the inital VM is setup and ready for the snapshot I run this command.

btrfs subvolume snapshot /mnt/cache/VMbtrfs /mnt/cache/VMs_backup

 

Does the reflink only work for refferences or can I use it for a new machine I make like the one below called 1070 instead of 1060

cp --reflink /mnt/cache/VMs_backup/1060/vdisk1.img /mnt/cache/VMs_backup/1070/vdisk1.img

 

and then 1080 for a third machine

cp --reflink /mnt/cache/VMs_backup/1060/vdisk1.img /mnt/cache/VMs_backup/1080/vdisk1.img

 

if it is making refference links, won't one change the other? Or does that were this command comes in to get a second instance of it?
btrfs send /mnt/cache/VMs_backup | btrfs receive /mnt/disk1

For what you're trying to do you don't need snapshots, just use cp --reflink, e.g. the original vdisk is:

 

/mnt/cache/domains/VMName/vdisk1.img

 

then just cp --reflink to create the other vdisks

 

cp --reflink /mnt/cache/domains/VMName/vdisk1.img /mnt/cache/domains/VMName2/vdisk1.img

cp --reflink /mnt/cache/domains/VMName/vdisk1.img /mnt/cache/domains/VMName3/vdisk1.img

etc

 

5 minutes ago, johnnie.black said:

For what you're trying to do you don't need snapshots, just use cp --reflink, e.g. the original vdisk is:

 

/mnt/cache/domains/VMName/vdisk1.img

 

then just cp --reflink to create the other vdisks

 

cp --reflink /mnt/cache/domains/VMName/vdisk1.img /mnt/cache/domains/VMName2/vdisk1.img

cp --reflink /mnt/cache/domains/VMName/vdisk1.img /mnt/cache/domains/VMName3/vdisk1.img

etc

 

Ahh okay. So maybe I am just over complicating things. And then if I install something on VMName2 it won't change VMName1?

15 minutes ago, johnnie.black said:

For what you're trying to do you don't need snapshots, just use cp --reflink, e.g. the original vdisk is:

 

/mnt/cache/domains/VMName/vdisk1.img

 

then just cp --reflink to create the other vdisks

 

cp --reflink /mnt/cache/domains/VMName/vdisk1.img /mnt/cache/domains/VMName2/vdisk1.img

cp --reflink /mnt/cache/domains/VMName/vdisk1.img /mnt/cache/domains/VMName3/vdisk1.img

etc

 

So my current disk is at

/mnt/cache/VMbtrfs/1060/vdisk.img

Running the below command:

cp --reflink /mnt/cache/VMbtrfs/1060/vdisk.img /mnt/user/VMbtrfs/650/vdisk1.img

I am getting error:

cp: failed to clone '/mnt/user/VMbtrfs/650/vdisk1.img' from '/mnt/cache/VMbtrfs/1060/vdisk.img': Invalid cross-device link

 

Is that command right? When I check the target location, the folder exists but not the file. Even if I create the file it is still the same error.

Oh der I think I found the problem.

path is different mount point.

21 minutes ago, johnnie.black said:

For what you're trying to do you don't need snapshots, just use cp --reflink, e.g. the original vdisk is:

 

/mnt/cache/domains/VMName/vdisk1.img

 

then just cp --reflink to create the other vdisks

 

cp --reflink /mnt/cache/domains/VMName/vdisk1.img /mnt/cache/domains/VMName2/vdisk1.img

cp --reflink /mnt/cache/domains/VMName/vdisk1.img /mnt/cache/domains/VMName3/vdisk1.img

etc

 

cp --reflink /mnt/cache/VMbtrfs/1060/vdisk.img /mnt/cache/VMbtrfs/650/vdisk.img

Yeah the first error was due to my pathing issue between user and cache instead. The above is now giving me this error I don't see where the problem is on that one though.
cp: failed to clone '/mnt/cache/VMbtrfs/650/vdisk.img' from '/mnt/cache/VMbtrfs/1060/vdisk.img': Invalid argument

Yeah, that should work, as long as the dest folder already exists, if you're copy/pasting try typing the command instead since the forum sometimes add extra characters on paste.